Okay, this has been on my mind the whole day. And after searching the entire internet, articles, youtube videos and what not, I cannot find a legitimate answer anywhere. So, I decided to post the question here myself. PLEASE NOTE: The question isn't why Allah didn't forgive Iblish when He forgave Adam (AS) and Eve (RA) for their sins. The Question is WILL ALLAH FORGIVE Iblish IF he decides to REPENT TO ALLAH (SWT). I came across a Dr. Zakir Nayek video during researching and while it did not answer the question (not even close) he mentioned that Allah (SWT) has filled Iblish's heart with sins (and Allah [SWT] knows the future- yes, undoubtedly). Why would He fill his heart with sins? Isn't it contradicting with the FREE WILL we Mankind and the Jinn possess? What if the Devil finally came to the realization of his horrible mistakes and decided to seek Allah's forgiveness? For indeed Allah is the most Merciful and the most Forgiving, will Allah (SWT) not forgive him? If no then why not?
Consider that this was Allah's (ﷻ) response to Pharaoh (Firown) when he "repented" after all his evil and the punishment overtook him: "Now? And you had disobeyed [Him] before and were of the corrupters" - Qur'an 10:90-91. In the end, Pharaoh's repentence was not accepted. I imagine the same would be the case for Iblis if he 'repented.'
Repenting when it is too late/inappropriate is fruitless.
Moreover, 'hypotheticals' are not real. Allah (ﷻ), the All Knowing and Seer of the Future, only declares something to be true when it is true. One example: he knew Abu Lahab would die upon disbelief, thus He declared this before he even died! (Sure people could think, "what if he repented"; but clearly he had no intention to and indeed did not! SubhanAllah).
Likewise, he declared Satan to be cursed.. which indicates Satan has no intention to repent and in fact will not repent!
"Why would He fill his heart with sins? Isn't it contradicting with the FREE WILL we Mankind and the Jinn possess?"
Whether Satan or anyone else (from humans or Jinn), Allah (ﷻ) only gives you what you choose. If you choose good, Allah (ﷻ) increases you in good. And if you choose evil, then you are increased in this as well. He says this in various places throughout the Qur'an. e.g., "In their hearts is disease, so Allah has increased their disease" - Qur'an 2:10.
Satan was envious of Adam.. to the point of refusing belief. He chose this for himself.
Allah forgives Adam and Eve by teaching them the Dua. That is because they only disobeyed. Iblees Was among angels when commanded to prostrate to Adam. All angels obeyed but Iblees refused claiming he was made of fire and better than Adam who was made of dust. This is arrogance so he was cursed for all time. Adam and Eve were forgiven. The first and worst crime is arrogance,
Many people answer by saying that Satan is cursed hence he will never repent. It is very unfortunate that all of the believers have misunderstood their Lord. The Lord is not like that, and there is a chance for the one who despaired, to repent and turn back. Anything is possible, as long as the fundamental principle of Allah's Oneness remains intact. The curse can be lifted, and the one who despaired, can be saved. There is a far bigger wisdom behind the creation of humanity, and iblis rebelled and declared enmity towards mankind due to his own misunderstanding. He can be saved, but another devil is then bound to take his place in misleading humanity. Allah is a God of Peace and Harmony and Justice, He does not take pleasure in punishing his creations. The command of prostration to adam was indeed a test for lucifer/iblis, but it was also a huge test for the angels as well, and yes, angels also have free will, but you were all misinformed. Iblis was bound to fall astray, but he can turn back. Once the true wisdom behind the creation of mankind comes to light, all the angels will have their faiths shaken, and most of them will swoon to the blast of the trumpet for this very reason. Never underestimate the mercy of God. I hate satan as much as anyone else, maybe even more. But redemption must come before destruction.