I use Proton as well and it's been great, but setting up their bridge for IMAP access in a way that worked for my setup was needlessly annoying (run on a headless server and access it from other devices within the network and docker containers on said server).
Fastmail and proton mail are usually recommended when this question comes up among technical groups.
I use Proton as well and it's been great, but setting up their bridge for IMAP access in a way that worked for my setup was needlessly annoying (run on a headless server and access it from other devices within the network and docker containers on said server).