My understanding is that mailbox.org is one of these services? But you still recommend them?
They just offer normal email features (TLS connections, PGP support, 2FA for webmail).
An "encrypted" service encrypts the messages at rest (on their server storage) but that makes it incompatible with normal email protocols which means you have to use their protocols and their apps to access it. Proton offers an adapter that allows you to use normal protocols (IMAP/POP3/SMTP) but it's only for PC, and if they ever discontinue that your email becomes captive.