The number of tutorials I have seen about spinning up a tor relay on a VPS is crazy. These tutorials are probably written by three letter agencies - though I have no proof.
Regardless, protonmail doesn’t let people register when connecting with Tor unless you use phone number or card to make a payment. You will have to give up something which identifies you, and so it really doesn’t matter when you connect with Tor after you have already registered - there is a way to connect who you are.