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?
And you keep herr/frau, so technically it would be Frau Professorin Doctor Jones.
Generally when opening an email you condense it, and simply refer to the person as “Sehr geehrte Frau Professorin Jones” - Very honoured ms. professor Jones. They’re very humble.