I've cancelled my subscription yesterday, conveniently it was about to renew at the end of the week, so I have a few days to migrate from Proton, here's what I'm thinking of, but I'd love to hear what other people are switching to
wanna add to the pile recommending mailbox.org. switched to their standard plan (4 eur a month, but you can go lower) recently exactly because of this whole mess and i have absolutely no regrets. finally got to use my domain for email and setting up a handful of aliases was a breeze. been getting good use of their caldav/webdav integrations, too.