Down 8 times in 36 fights it's looking rough. Sure he can get up, but that's recovery and heart not chin. A tough chin won't be put down or stumbled in the first place
Chin isn't quite as suspect as Aj, but it's far from granite Though unlike Aj he has a set of balls and great recovery. He doesn't go gun shy for many fights after getting hurt, dropped Fury's character outside the ring at times is despicable and maybe a little cowardly, but inside? He's a warrior
Fury has a granite skull, Wilder landed on it many times but he never seemed hurt at all. Chin itself is suspect.
It's good enough with his poise and recovery to get by almost everyone's scary moment chin-check without getting straight KO'd still, probably. But I still think AJ has a good chance to stop him. A very good chance. He never had a particularly/uniquely good chin like a Mercer or Vittles. He never even really had a Lennox-level chin.
Chin has always been average, he's been dropped and hurt by too many fighters to suggest he ever had a genuinely good chin. But his powers of recovery are near supernatural if you give him a moment to recover. The 9th round against Usyk really showed the difference between a fighter who knows how to finish and a fighter who doesn't when we compare it to the Wilder knockdowns. Usyk was able to sustain his attack after hurting him, not allowing Fury time to recover and had Fury the closest to being stopped we've ever seen, if not for the referee it might have ended in the 9th. Wilder in contrast, who no doubt hits way harder than Usyk couldn't capitalise on his advantage and got caught coming it to finish it twice in the first fight, allowing Fury that moment to clear his head.