I switched to Protonmail years ago after learning that the US courts had ruled that third-party email hosts like Gmail do not receive Fourth Amendment protections. I had originally intended to fully self-host, but between the effort required to maintain my own email server and keep it off blacklists, I was looking specifically for something hosted outside direct US jurisdiction and that wasn't "responsive" to informal requests from the US.
Protonmail isn't exactly that, as I expect they would answer a subpeona, but that's OK. I'm not doing anything that I need to truly hide from the state; I only wanted my normal correspondence to not be vacuumed up with everyone else's by the NSA. At least the information that they have access to (and is therefore discoverable) is limited by design.
Their security posture also means that some of their other products - calendar, in particular - are virtually useless to me. Email not being available via IMAP is a bummer, but manageable since they have decent native apps for the platforms I care about. The only exception to that is visionOS; their iOS and iPadOS apps aren't installable on the Vision Pro, so I'm left using the web client there.