The advice I use for myself is always assume a service will either turn shitty enough that you need to leave, or just shut down due to some reason, so I try and only use services that make it easy to move away from.

So instead of Proton or Tuta, use a normal email provider that provides IMAP and supports a custom domain name. There are good ones around for privacy and features like Mailbox.org or similar.

A domain is ~$12/year and ensures you (hopefully) never need to change a bunch of emails on accounts again even if moving to a different email provider.