If encryption is a must, then use Tuta. German company, privacy focused, open source all around, no surveillance, free tier with encryption available, encrypted calendars, accessible paid subscriptions with actually useful services.
Keep a proton for situations where you can actually use the encryption. Most of the time the encryption is as useless as a VPN.
Also keep in mind all it is is pgp with a directory lookup. I think proton made their pgp directory lookup more open in the last few years, so it may not have any real benefits.