The Qur'an only endorses the Torah and the Gospel that have been revealed by Allah, not the versions that are among us now, which we believe contain both a version of the truth as well as corruption.
The quote you posted is a very long quote in specific, and the topic is a wide topic in general, to address in one post. So, I will answer you with titles. Any particular verse or topic that you want to discuss further or in more details, please post a separate question for each verse.
To summarize, in Islam, we have six articles of faith that we have to believe in, and one of them is the Scripture revealed by Allah to previous messengers:
آمَنَ الرَّسُولُ بِمَا أُنزِلَ إِلَيْهِ مِن رَّبِّهِ وَالْمُؤْمِنُونَ كُلٌّ آمَنَ بِاللَّهِ وَمَلَائِكَتِهِ وَكُتُبِهِ وَرُسُلِهِ لَا نُفَرِّقُ بَيْنَ أَحَدٍ مِّن رُّسُلِهِ وَقَالُوا سَمِعْنَا وَأَطَعْنَا ۖ غُفْرَانَكَ رَبَّنَا وَإِلَيْكَ الْمَصِيرُ
The Messenger has believed in what was revealed to him from his Lord, and [so have] the believers. All of them have believed in Allah and His angels and His books and His messengers, [saying], "We make no distinction between any of His messengers." And they say, "We hear and we obey. [We seek] Your forgiveness, our Lord, and to You is the [final] destination."
— Surat Al-Baqarah 2:285
I have highlighted the phrase "the Scripture revealed by Allah" as this answers almost all the questions about the verses you mentioned. We believe that Allah revealed Scripture to previous people and that they were entrusted to preserve as revealed (see Qur'an 5:44), but they corrupted their Scripture.
The article you quoted said that there are some Muslims who contend that Surat Al-Baqarat 2:140 is the only reference to previous Scripture being corrupted. Actually the phrase about "concealing a testimony" is about knowing that a prophet would come from that area, and the Jewish tribes mentioning that over and over to the Arabs, but when the Prophet ﷺ came to them, they rejected him for not being from the tribe of Levi (or any of the 12 tribes for that matter). Having said that, the verses in the Qur'an and the hadiths that talk about the corruption of previous Scripture are numerous. Such corruption took different forms, and I am going to use verses from the Qur'an alone (no reference to hadiths at this stage) to address your part of the question about the assumption that nowhere in the Qur'an is a mention of former Scriptures having been corrupted:
Deletions through concealing parts of the revelation:
وَمَا قَدَرُوا اللَّهَ حَقَّ قَدْرِهِ إِذْ قَالُوا مَا أَنزَلَ اللَّهُ عَلَىٰ بَشَرٍ مِّن شَيْءٍ ۗ قُلْ مَنْ أَنزَلَ الْكِتَابَ الَّذِي جَاءَ بِهِ مُوسَىٰ نُورًا وَهُدًى لِّلنَّاسِ ۖ تَجْعَلُونَهُ قَرَاطِيسَ تُبْدُونَهَا وَتُخْفُونَ كَثِيرًا ۖ وَعُلِّمْتُم مَّا لَمْ تَعْلَمُوا أَنتُمْ وَلَا آبَاؤُكُمْ ۖ قُلِ اللَّهُ ۖ ثُمَّ ذَرْهُمْ فِي خَوْضِهِمْ يَلْعَبُونَ
And they did not appraise Allah with true appraisal when they said, " Allah did not reveal to a human being anything." Say, "Who revealed the Scripture that Moses brought as light and guidance to the people? You [Jews] make it into pages, disclosing [some of] it and concealing much. And you were taught that which you knew not — neither you nor your fathers." Say, " Allah [revealed it]." Then leave them in their [empty] discourse, amusing themselves.
— Surat Al-An'am 6:91
الَّذِينَ آتَيْنَاهُمُ الْكِتَابَ يَعْرِفُونَهُ كَمَا يَعْرِفُونَ أَبْنَاءَهُمْ ۖ وَإِنَّ فَرِيقًا مِّنْهُمْ لَيَكْتُمُونَ الْحَقَّ وَهُمْ يَعْلَمُونَ
Those to whom We gave the Scripture know him as they know their own sons. But indeed, a party of them conceal the truth while they know [it].
— Surat Al-Baqarah 2:146
Additions through claiming that some scripture written by people who are neither prophets nor messengers was a revelation from God (in reference to the canonized Gospels we have today as none of them are Jesus's Gospel, and in reference to the epistles of Paul, Peter, and John, and the Revelation):
وَإِنَّ مِنْهُمْ لَفَرِيقًا يَلْوُونَ أَلْسِنَتَهُم بِالْكِتَابِ لِتَحْسَبُوهُ مِنَ الْكِتَابِ وَمَا هُوَ مِنَ الْكِتَابِ وَيَقُولُونَ هُوَ مِنْ عِندِ اللَّهِ وَمَا هُوَ مِنْ عِندِ اللَّهِ وَيَقُولُونَ عَلَى اللَّهِ الْكَذِبَ وَهُمْ يَعْلَمُونَ
And indeed, there is among them a party who alter the Scripture with their tongues so you may think it is from the Scripture, but it is not from the Scripture. And they say, "This is from Allah," but it is not from Allah. And they speak untruth about Allah while they know.
— Surat Al 'Imran 3:78
Changing the content of what has been revealed by Allah:
مِّنَ الَّذِينَ هَادُوا يُحَرِّفُونَ الْكَلِمَ عَن مَّوَاضِعِهِ وَيَقُولُونَ سَمِعْنَا وَعَصَيْنَا وَاسْمَعْ غَيْرَ مُسْمَعٍ وَرَاعِنَا لَيًّا بِأَلْسِنَتِهِمْ وَطَعْنًا فِي الدِّينِ وَلَوْ أَنَّهُمْ قَالُوا سَمِعْنَا وَأَطَعْنَا وَاسْمَعْ وَانظُرْنَا لَكَانَ خَيْرًا لَّهُمْ وَأَقْوَمَ وَلَٰكِن لَّعَنَهُمُ اللَّهُ بِكُفْرِهِمْ فَلَا يُؤْمِنُونَ إِلَّا قَلِيلًا
Among the Jews are those who distort words from their [proper] usages and say, "We hear and disobey" and "Hear but be not heard" and "Ra'ina," twisting their tongues and defaming the religion. And if they had said [instead], "We hear and obey" and "Wait for us [to understand]," it would have been better for them and more suitable. But Allah has cursed them for their disbelief, so they believe not, except for a few.
— Surat An-Nisa' 4:46
Changing the concept (implied change of Scripture) of what has been revealed to them, e.g., by claiming that Jesus is God:
لَقَدْ كَفَرَ الَّذِينَ قَالُوا إِنَّ اللَّهَ هُوَ الْمَسِيحُ ابْنُ مَرْيَمَ ۖ وَقَالَ الْمَسِيحُ يَا بَنِي إِسْرَائِيلَ اعْبُدُوا اللَّهَ رَبِّي وَرَبَّكُمْ ۖ إِنَّهُ مَن يُشْرِكْ بِاللَّهِ فَقَدْ حَرَّمَ اللَّهُ عَلَيْهِ الْجَنَّةَ وَمَأْوَاهُ النَّارُ ۖ وَمَا لِلظَّالِمِينَ مِنْ أَنصَارٍ
They have certainly disbelieved who say, " Allah is the Messiah, the son of Mary" while the Messiah has said, "O Children of Israel, worship Allah, my Lord and your Lord." Indeed, he who associates others with Allah - Allah has forbidden him Paradise, and his refuge is the Fire. And there are not for the wrongdoers any helpers.
— Surat Al-Ma'idah 5:72
If this is indeed the case, the question arises as to why then in multiple verses there is what appears to some as a form of endorsement. In addressing the verses you mentioned, I will refer to Taysīr Al-Karīm Ar-Rahmān, the tafsīr (exegesis) of the Qur'an by Abdur-Rahman ibn Nasir As-Sa'di. If you want to discuss any specific verse in more details and refer to multiple exegeses for comparison and study, then please post a separate question for each verse:
Surat Al-Baqarah 2:136 explicitly restricts our belief to what has been revealed, not what the people of the Scripture now have in their hands, and indeed we are commanded to make no distinction between any of Allah's revelations:
قُولُوا آمَنَّا بِاللَّهِ وَمَا أُنزِلَ إِلَيْنَا وَمَا أُنزِلَ إِلَىٰ إِبْرَاهِيمَ وَإِسْمَاعِيلَ وَإِسْحَاقَ وَيَعْقُوبَ وَالْأَسْبَاطِ وَمَا أُوتِيَ مُوسَىٰ وَعِيسَىٰ وَمَا أُوتِيَ النَّبِيُّونَ مِن رَّبِّهِمْ لَا نُفَرِّقُ بَيْنَ أَحَدٍ مِّنْهُمْ وَنَحْنُ لَهُ مُسْلِمُونَ
Say, [O believers], "We have believed in Allah and what has been revealed to us and what has been revealed to Abraham and Ishmael and Isaac and Jacob and the Descendants and what was given to Moses and Jesus and what was given to the prophets from their Lord. We make no distinction between any of them, and we are Muslims [in submission] to Him."
— Surat Al-Baqarah 2:136
Surat Ali 'Imran 3:2-3 uses the phrases nazzala (Arabic: نزل) to mean His revelation and ma bayn yadayh (Arabic: لما بين يديه) which means what he had with him, which the verse clarifies right after that the Scripture being referred to is the Torah and the Gospel that Allah had revealed:
اللَّهُ لَا إِلَٰهَ إِلَّا هُوَ الْحَيُّ الْقَيُّومُ نَزَّلَ عَلَيْكَ الْكِتَابَ بِالْحَقِّ مُصَدِّقًا لِّمَا بَيْنَ يَدَيْهِ وَأَنزَلَ التَّوْرَاةَ وَالْإِنجِيلَ
Allah — there is no deity except Him, the Ever-Living, the Sustainer of existence. He has sent down upon you, [O Muhammad], the Book in truth, confirming what was before it. And He revealed the Torat and the Gospel.
— Surat Al 'Imran 3:2-3
Surat An-Nisa 4:136 again talks about the Scripture that Allah had sent, not what the people of the Scripture have in their hands right now or then:
يَا أَيُّهَا الَّذِينَ آمَنُوا آمِنُوا بِاللَّهِ وَرَسُولِهِ وَالْكِتَابِ الَّذِي نَزَّلَ عَلَىٰ رَسُولِهِ وَالْكِتَابِ الَّذِي أَنزَلَ مِن قَبْلُ وَمَن يَكْفُرْ بِاللَّهِ وَمَلَائِكَتِهِ وَكُتُبِهِ وَرُسُلِهِ وَالْيَوْمِ الْآخِرِ فَقَدْ ضَلَّ ضَلَالًا بَعِيدًا
O you who have believed, believe in Allah and His Messenger and the Book that He sent down upon His Messenger and the Scripture which He sent down before. And whoever disbelieves in Allah, His angels, His books, His messengers, and the Last Day has certainly gone far astray.
— Surat An-Nisa' 4:136
Surat Al-Ma'idah 5:47 again is asking Christians to judge by what Allah has revealed in the Gospel, which َQur'an 7:157 says it is to follow the prophet that they have in their Torah and their Gospel:
وَلْيَحْكُمْ أَهْلُ الْإِنجِيلِ بِمَا أَنزَلَ اللَّهُ فِيهِ وَمَن لَّمْ يَحْكُم بِمَا أَنزَلَ اللَّهُ فَأُولَٰئِكَ هُمُ الْفَاسِقُونَ
And let the People of the Gospel judge by what Allah has revealed therein. And whoever does not judge by what Allah has revealed — then it is those who are the defiantly disobedient.
— Surat Al-Ma'idah 5:47
Note that this verse is contextual, as the following verse says that the Qur'an is the one that supersedes, abrogates, and overrules all previous Scripture, but the article you quotes skipped that specific verse.
Surat Al-Ma'idah 5:49 again is talking about what Allah has revealed, and this verse, in particular, goes further to forbid the Prophet ﷺ from following their inclinations
وَأَنِ احْكُم بَيْنَهُم بِمَا أَنزَلَ اللَّهُ وَلَا تَتَّبِعْ أَهْوَاءَهُمْ وَاحْذَرْهُمْ أَن يَفْتِنُوكَ عَن بَعْضِ مَا أَنزَلَ اللَّهُ إِلَيْكَ ۖ فَإِن تَوَلَّوْا فَاعْلَمْ أَنَّمَا يُرِيدُ اللَّهُ أَن يُصِيبَهُم بِبَعْضِ ذُنُوبِهِمْ ۗ وَإِنَّ كَثِيرًا مِّنَ النَّاسِ لَفَاسِقُونَ
And judge, [O Muhammad], between them by what Allah has revealed and do not follow their inclinations and beware of them, lest they tempt you away from some of what Allah has revealed to you. And if they turn away — then know that Allah only intends to afflict them with some of their [own] sins. And indeed, many among the people are defiantly disobedient.
— Surat Al-Ma'idah 5:49
Surat Al-Ma'idah 5:50-52 have nothing to do with the corruption of the Scripture as such. They talk about them not willing to abide by what Allah has revealed to the Prophet ﷺ in the Qur'an:
أَفَحُكْمَ الْجَاهِلِيَّةِ يَبْغُونَ وَمَنْ أَحْسَنُ مِنَ اللَّهِ حُكْمًا لِّقَوْمٍ يُوقِنُونَ يَا أَيُّهَا الَّذِينَ آمَنُوا لَا تَتَّخِذُوا الْيَهُودَ وَالنَّصَارَىٰ أَوْلِيَاءَ ۘ بَعْضُهُمْ أَوْلِيَاءُ بَعْضٍ وَمَن يَتَوَلَّهُم مِّنكُمْ فَإِنَّهُ مِنْهُمْ ۗ إِنَّ اللَّهَ لَا يَهْدِي الْقَوْمَ الظَّالِمِينَ فَتَرَى الَّذِينَ فِي قُلُوبِهِم مَّرَضٌ يُسَارِعُونَ فِيهِمْ يَقُولُونَ نَخْشَىٰ أَن تُصِيبَنَا دَائِرَةٌ فَعَسَى اللَّهُ أَن يَأْتِيَ بِالْفَتْحِ أَوْ أَمْرٍ مِّنْ عِندِهِ فَيُصْبِحُوا عَلَىٰ مَا أَسَرُّوا فِي أَنفُسِهِمْ نَادِمِينَ
Then is it the judgement of [the time of] ignorance they desire? But who is better than Allah in judgement for a people who are certain [in faith]. O you who have believed, do not take the Jews and the Christians as allies. They are [in fact] allies of one another. And whoever is an ally to them among you — then indeed, he is [one] of them. Indeed, Allah guides not the wrongdoing people. So you see those in whose hearts is disease hastening into [association with] them, saying, "We are afraid a misfortune may strike us." But perhaps Allah will bring conquest or a decision from Him, and they will become, over what they have been concealing within themselves, regretful.
— Surat Al-Ma'idah 5:50-52
Surat Yunus 10:94 does not talk about consulting previous Scripture; rather, it is talking about consulting those who read or studied previous Scripture, as the Prophet ﷺ did when he got his first revelation and consulted Waraka ibn Nawfal who told him that he had the signs of the prophet that was mentioned in the Torah of Moses. Having said that, the verse is contextual and is referring to specific Jews who embraced Islam, e.g., Ka'b al-Ahbār and 'Abdullah ibn Salām:
فَإِن كُنتَ فِي شَكٍّ مِّمَّا أَنزَلْنَا إِلَيْكَ فَاسْأَلِ الَّذِينَ يَقْرَءُونَ الْكِتَابَ مِن قَبْلِكَ لَقَدْ جَاءَكَ الْحَقُّ مِن رَّبِّكَ فَلَا تَكُونَنَّ مِنَ الْمُمْتَرِينَ
So if you are in doubt, [O Muhammad], about that which We have revealed to you, then ask those who have been reading the Scripture before you. The truth has certainly come to you from your Lord, so never be among the doubters.
— Surat Yunus 10:94
Surat Al-Anbya 21:7 is not asking Muslims to confer with the people of the Scripture; rather, it is addressing the disbelievers from among the Arabs who rejected the idea that Allah would send a human being as His messenger instead of sending an angel. The verse commands the disbelievers to confer with the people of the Scripture (who were living among them at the time) to check if previous messengers were men or angels; it is not to confer about their creed at large:
وَمَا أَرْسَلْنَا قَبْلَكَ إِلَّا رِجَالًا نُّوحِي إِلَيْهِمْ ۖ فَاسْأَلُوا أَهْلَ الذِّكْرِ إِن كُنتُمْ لَا تَعْلَمُونَ
And We sent not before you, [O Muhammad], except men to whom We revealed [the message], so ask the people of the message if you do not know.
— Surat Al-Anbya 21:7
Surat Al-'Ankabut 29:46 is not talking about question the authority of the Scriptures of the Christians at all; rather, it is about how Muslims should invite others to Islam when debating with the people of the Scripture (in a way that is best, except for those who commit injustice among them). As for the belief, again it is about what was revealed and not what they have among them now or then:
وَلَا تُجَادِلُوا أَهْلَ الْكِتَابِ إِلَّا بِالَّتِي هِيَ أَحْسَنُ إِلَّا الَّذِينَ ظَلَمُوا مِنْهُمْ ۖ وَقُولُوا آمَنَّا بِالَّذِي أُنزِلَ إِلَيْنَا وَأُنزِلَ إِلَيْكُمْ وَإِلَٰهُنَا وَإِلَٰهُكُمْ وَاحِدٌ وَنَحْنُ لَهُ مُسْلِمُونَ
And do not argue with the People of the Scripture except in a way that is best, except for those who commit injustice among them, and say, "We believe in that which has been revealed to us and revealed to you. And our God and your God is one; and we are Muslims [in submission] to Him."
— Surat Al-'Ankabut 29:46