Depends. In real life, simply he/him. Online, either he/him or, if someone would ask, any gender-neutral pronoun people wanna use (they/them, ne/nem, xe/xem, even it/its, but please not shi/hir, that has some connotations I don't identify with).
I don't think one ever has asked me, though - on most internet platforms, people either know that I'm ftm and therefore use male pronouns, or don't know and simply guess and I correct them if they use female forms, or use they/them anyway.
I'm a linguist by profession, I don't take language usage too personally
So I normally don't bother about these things.
Also, I live in Germany, so we don't have gender-neutral pronouns here that people would actually use, only equivalents of he, she, it, and no one would use the latter for these purposes.