I carried out the procedure you mention before I commented here. The good news is that it's working again with TOR. Btw. The address looks more or less so https://mail.protonmailrmez3lotccipshtkleegeto…………………ozyd.onion
Great! It still doesn't work in default tor browser settings for me. Cookies, sessionstorage and localstorage are needed for it to work. Perhaps the tor mode in brave browser is the easy way, dunno I don't have brave on my computer to try it rn.