Tony never redeemed himself
There was an interesting essay online describing a main character's redemption arc: The character acknowledges their mistakes or wrongdoings, apologizes to those hurt, and tries to make amends. A character who was offered as a good example of a redemption arc is Prince Zuko of Avatar. Among the characters who were shown not to have redeemed themselves was Tony Stark. Tony had years after Civil War to acknowledge his mistakes, to apologize to May, Peter, Team Cap, and everyone else, and to make amends for his actions. Tony did none of this. Ironically, it's alleged that Tony Stark's portrayer is the one who made Tony die unredeemed. Allegedly the original Endgame script had Tony having an epiphany after he's rescued and apologizing, but what we got instead was a delusional rant that in typical Tony fashion blames everyone but the real cause of the problem: Tony.
Note: I've never seen Good Omens so these characters are probably out of character.
*****
"One snap does not redeem a lifetime of recklessness and disregard," the angel Aziraphale said primly. He continued, "The weapons made by his hands, the decisions that served only his own needs, and his unrepentant hypocrisy all banish him from the Pearly Gates. And in life this man made remarks full of a kind of careless cruelty that is far more representative of your realm than mine, Crowley."
Before the demon could reply, Aziraphale folded his hands and said, "The matter is settled. Anthony Edward Stark will never see Heaven."
Crowley shook his head, crossed his arms, and said, "Well I'm not having it. I don't care if Stark's actions and inventions---especially that egotistical floating Satellite of Spying and Death---guarantee that Stark was NOT on the side of the angels. We have standards too, you know. And admitting this egotistical blowhard into the Hellfire Club will not happen, not even when all Lucifer's minions get frostbite."
The angel and the demon stared at each other a moment, then turned to look at Tony Stark's soul. Stark rolled his eyes at them. He'd probably have mocked them, but two layers of magical adhesive---one from each immortal judge---kept his mouth shut. Stark hadn't lasted 10 seconds in the afterlife before he'd been shut up by two beings who had better things to do than listen to Tony Stark's "humor."
Aziraphale said, "We seem to be at an impasse."
Crowley narrowed his eyes and said, "Well, there's always the third option..."
*****
Appropriately, they ended up in Death Valley. Aziraphale transported them there, while Crowley did Stark's transformation.
When Crowley was done he released the bindings on Stark's mouth. The man-turned-donkey brayed his displeasure and stomped one hoof.
Aziraphale asked, "You're sure he'll blend in?"
Crowley nodded and answered, "This whole area's full of burros. One more won't make any difference. And without an opposable thumb or his multi-billions, Stark won't be able to cause too much trouble."
Aziraphale nodded and asked, "So how long will Stark be like that?"
Crowley shrugged and said, "That's up to Stark. He'll stay a donkey until he learns to stop being such a jackass."
After the angel and demon watched Stark unsuccessfully try to kick them, Aziraphale said, "You'll check in on him next millennia, then?"
"Yes," Crowley said as he wrapped an arm around the angel's shoulders. He continued, "How about we stop for a bite? There's a diner nearby called Indian Tacos and Shaved Ice."
As the two beings disappeared, Tony Stark was left to contemplate his just reward.