This touches on both Molinism and the Problem of Evil, with explanations here:
Molinism:
Molinism differs from Calvinism by affirming that God grants salvation, but a person has the choice to freely accept it or reject it (but God knows that if the person were put in a particular situation he or she would not reject it).
Pretty sound Arminianism, eh? But in the end there are people in hell who could be saved if GOD would just wait for them to repent.
HE waits for some until they are 80-100 years old but others HE cuts short at 20 or 50 years or even in the womb? Why not wait and give everyone an equal chance to to accept HIM? Something is wrong with this theory....
We also know HE wants everyone to be saved and that
HIS perfect love is perfectly patient, 1 Cor 13:4 Berean Standard Bible, Love is patient, love is kind.
so once hell is full of those HE has condemned, why does not HIS perfect love wait for those in hell to give up their foolish rebellion and ask for salvation?
The only answer is that some are so immersed in their enslavement to the addiction of sin that they can't ever repent or ask HIM for salvation!
Everyone who can be saved from eternal hell will be saved from hell, not matter how they feel about it while enslaved to sin!!! Only those who CANNOT accept the gospel will be condemned, NOT those who don't want to accept the gospel at some time in their lives and died too son to repent.
The unforgivable Sin
From my Christian pov, the unforgivable sin was the Satanic fall, their free will decision to reject by faith, ie, an unproven hope, (NOT proof) that YHWH's claims to be our creator GOD and to reject the gospel of salvation from sin as found only in the Son. It contained the ideas that HE was no better than the rest of us so HE must be a liar and as a liar, a false god...just listen to atheists and pagans about their opinion of HIM for confirmation.
As the first liar in all of creation, HE must therefore be the most evil person in existence so they repudiated HIM, rejecting HIM from having any influence in their lives at all. Putting their faith in this idea that HE was evil and driven by a psychotic megalomania made them eternally unfit to ever be HIS Bride so they were condemned to judgement on the spot, passed over for election to salvation due to their choice.
They can't be forgiven because
1. they made the decision to rebel against GOD's claims to Deity by their free will and a free will decision cannot be changed by anyone, even GOD, unless the person asks for it to be changed. All free will decisions must be sacrosanct and inviolable, apart from GOD's interference or it cannot be defined as free. This is not a rule but a matter of definition: A cannot be not A at the same time; wet cannot be dry at the same time; free to choose an unchangeable decision can't therefore be changed by another and still be considered free.
2. Once they rebelled they became enslaved by the addictive power of evil which destroyed their ability to seek true repentance and save themselves by changing their minds about HIM. They were instantly and totally unable to repent of their evil and became even more committed to the belief that they were right to rebel against this upstart liar and false god. So great is their addiction to evil that even after they learned the truth of HIS divinity and power when they saw the creation of the physical universe with their own eyes as described in Job 38:7, they could not change their minds because they loved their sin more than the truth as we learn in Roman 1:20+.
This describes the Satanic fall that precipitated the war in heaven and had all sinners, elect and reprobate, flung into the earth.