In the Tafsir of Ibn Kathir for verse 50:6, he says the following:
أَفَلَمْ يَنظُرُواْ إِلَى السَّمَآءِ فَوْقَهُمْ كَيْفَ بَنَيْنَـهَا وَزَيَّنَّـهَا
Have they not looked at the heaven above them, how We have made it and adorned it,
With lamps;
وَمَا لَهَا مِن فُرُوجٍ
and there are no Furuj in it
I.e., clefts, according to Mujahid. Others said that Furuj means, rifts, or cracks. All these meanings are close to one another. Allah the Exalted and Most Honored said,
الَّذِى خَلَقَ سَبْعَ سَمَـوَتٍ طِبَاقًا مَّا تَرَى فِى خَلْقِ الرَّحْمَـنِ مِن تَفَـوُتٍ فَارْجِعِ الْبَصَرَ هَلْ تَرَى مِن فُطُورٍ - ثُمَّ اْرجِعِ البَصَرَ كَرَّتَيْنِ يَنقَلِبْ إِلَيْكَ البَصَرُ خَاسِئًا وَهُوَ حَسِيرٌ
Who has created the seven heavens one above another; you can see no fault in the creation of the Most Gracious. Then look again: "Can you see any rifts" Then look again and yet again, your sight will return to you in a state of humiliation and worn out (67:2-4)
Fatigued, unable to discover any imperfection or shortcomings. The statement of Allah the Exalted, the Blessed,
- Tafsir Ibn Kathir
He seems to imply that both verses you quotes give similar meaning. In verse 50:6, Allah is telling the disbelievers to look at the creations of Allah, to find mistakes in it. Verses 50:2-6 reads the following:
˹All will be resurrected,˺ yet the deniers are astonished that a warner has come to them from among themselves ˹warning of resurrection˺. So the disbelievers say, “This is an astonishing thing! ˹Will we be returned to life,˺ when we are dead and reduced to dust? Such a return is impossible.” We certainly know what the earth consumes of them ˹after their death˺, and with us is a well-preserved Record. In fact, they reject the truth when it has come to them, so they are in a confused state. Have they not then looked at the sky above them: how We built it and adorned it ˹with stars˺, leaving it flawless?
- Dr. Mustafa Khattab, The Clear Quran
In verse 67:3, Allah is glorifying Himself in the Quran, and asks us to look at the creations of the One worthy of all glory, and see if there are mistakes in it. Verses 67:1-3 reads the following:
Blessed is the One in Whose Hands rests all authority. And He is Most Capable of everything. ˹He is the One˺ Who created death and life in order to test which of you is best in deeds. And He is the Almighty, All-Forgiving. ˹He is the One˺ Who created seven heavens, one above the other. You will never see any imperfection in the creation of the Most Compassionate. So look again: do you see any flaws?
- Dr. Mustafa Khattab, The Clear Quran
Tafsir Ibn Kathir for verse 67:3 states:
فَارْجِعِ الْبَصَرَ هَلْ تَرَى مِن فُطُورٍ
Then look again. Can you see any rifts
Meaning, look at the sky and pay close attention to it. Do you see any flaw, deficiency, defect or rifts in it Ibn `Abbas, Mujahid, Ad-Dahhak, Ath-Thawri and others said concerning Allah's statement,
فَارْجِعِ الْبَصَرَ هَلْ تَرَى مِن فُطُورٍ
Then look again. Can you see any rifts
That it means cracks
- Tafsir Ibn Kathir
Verse 67:3 is simply saying that Allah created everything, including the heavens, and asks us to look at His creations, and try find errors in it. He then states that no matter how much we look, we will never find mistakes in the creation of Allah, whether it is on the earth, the earth itself, or the heavens.
Verse 50:6 is asking us to look at 'ٱلسَّمَآءِ', which either means 'heavens' or 'sky', and in this case, it's more acceptable to accept that Allah means 'sky'. This is also the word Dr. Mustafa Khattab opts to go for in his translation for the Quran, but of course, Allah knows best.