I think we can ignore Fury's performance against Ngannou, he has always fought down to the level of his opposition and there's no way he prepared properly for that one. He's visibly in much better shape now than then.
It's possible Fury has gone over the hill due to his lifestyle but Usyk is 37 and didn't look all that great against Dubois.
I've always thought Fury would just be too big for Usyk because unlike Joshua he can maintain range with his jab and then hold and tie up effectively at short range to then lean on the smaller man. Joshua took plenty of rounds off Usyk and Fury is a better boxer than AJ.
So I think Fury by decision assuming both are a little post-prime, if either is fully post-prime then he loses but that's hard to gauge as both have been inactive and are getting older.