Doesn't the Quran say that Allah forgives all sins?

The Quran presents a duality regarding forgiveness, claiming both that Allah forgives all sins and that certain sins, particularly apostasy, result in eternal damnation. In Surah 39:53-54, believers are encouraged not to despair of Allah's mercy, suggesting a universal offer of forgiveness. However, Surah 3:86-91 complicates this by stating that those who disbelieve after having believed will not have their repentance accepted, indicating a limit to Allah's forgiveness. This inconsistency leads to confusion about the conditions under which forgiveness is granted. The text oscillates between offering hope for repentance and declaring a finality to the fate of apostates, ultimately presenting a contradictory view of divine mercy and justice.