I just took this grey squirrel photo on the off-chance, and was rather pleased that it came out pretty well. ISO25600 is far from ideal, and it has been got at by Topaz AI (which, when it works, definitely works!).
Canon R6 + RF 600mm lens
Kept dark as it seemed to suit.
I would love to see what kind of noise that had before you threw it at Topaz. I assume Topaz AI is an anti-noise thing.