I switched from ProtonMail after a few months (despite having paid up front for a year) because the UX is so bad. You are forced to use their client apps, which are full of annoying bugs and design flaws. They ignored my support requests. Eventually I switched to MailFence, which has even worse UIs, straight out of the 90s, but you can use any IMAP client so it doesn’t really matter. (ProtonMail does have a bridge tool so you can use IMAP, but only on a desktop OS.) Still on the lookout for something better.