Of course. Appeal to authority was never a fallacy; the fallacy is "appeal to false authority". "Terry Tao knows much more about math in general and this in particular than I do, so I'll trust what he says here" is completely valid.

A fields medal doesn't indicate general authority in mathematics, only authority with regards to what was necessary for getting the medal.

OK, but being a math professor does indicate general authority in mathematics.

Appeal to authority is a dumb logical fallacy in reality geniuses are better at everything and we should prioritize their opinions by some decent weight over everyone else. Obviously.