Allah's eternal punishment is undeserving

As-salamu alaykum wa rahmatullahi wa barakatuh, I hope this message finds you well. I have a question that has been deeply troubling me and affecting my faith, and I sincerely seek your guidance and knowledge. I am struggling to understand how Allah, who is Al-Rahman (The Most Merciful), can punish someone for eternity in Hell. If a person lives for a short time in this world — perhaps 70 or 80 years — how can their mistakes, no matter how great, justify an eternal punishment? From my understanding, even if someone fully knows the truth of Islam yet rejects it until death, the concept of eternal punishment feels difficult to reconcile with Allah’s infinite mercy. In my human perspective, I feel that I would never punish someone endlessly for a finite lifetime of mistakes. Of course, I know my understanding is limited, but this creates a deep conflict in my heart. The only reasoning I can think of is that perhaps the soul, even after being in Hell for unimaginable lengths of time, still refuses to accept Allah — but then again, Allah created us and has complete power over our nature. Could He not have created us all to eventually enter Jannah, even if at different levels, so that His perfect justice and perfect mercy are both fulfilled? I ask this question with humility and sincerity, not out of disrespect, but because I genuinely wish to understand and strengthen my iman. I would be deeply grateful for your explanation. JazakAllahu khayran