Like many others here, for me, it depends on how much of an effort they‘re putting forth.
If it were somebody I knew who actually seemed to be suffering from gender dysphoria and put forth an effort to pass, sure, why not if it makes them feel better.
If it’s somebody who already passes (or mostly passes) and I’ve never known them as anything else, it would actually feel weird to refer to them otherwise.
But if it’s somebody like Kevin Gibes, on the other hand, no. It feels too much like somebody asking to be referred to by a “cool” nickname they made up themselves.
And if anyone wants to be referred to by a neutral or made-up pronoun, their pronouns are a moot point because I’ll be distancing myself as far from them as possible, as well as avoiding any mutual contacts.