Can a PhD (Or a doctorate or an MD) choose to use a gendered title instead of Dr? For example, suppose an AFAB PhD comes out as a trans man. Is he allowed to use Mister to affirm his gender? Or is he stuck in the gender neutral Doctor zone forever? Does he have to get knighted by the British monarchy in order to get a masculine title?
“Doctor” is a title you become entitled to use by virtue of holding a PhD - you have the option to use it, but nothing compels you to do so if you don’t want to.
Note that the reverse isn’t true - representing yourself as holding a doctorate when you don’t can be a fairly serious crime - if you did for the purposes of getting money from some, then it’s probably some kind of fraud