Proton Mail is a good idea for the zero-knowledge encryption, but it’s a whole lot of vendor lock in as you can’t use standard clients (IMAP/STMP/CalDAV/CardDAV) for mail/calendar/contacts. Tuta isn’t any better in this regard. If you’re looking for ability to use standard open clients, probably mailbox.org would be a good option to check out.

They have really dragged out making a Linux Drive client. The protocol isn’t documented for 3rd party implementations, but they’re Windows/Mac desktop clients are open source so it’s conceivable to reverse engineer the protocol from those, but nobody has done it.

They’ve delivered a bunch of new apps to their suite like a crypto wallet and an AI agent, rather than addressing popular feature requests for existing software.