The only other secure location I have heard is Tuta Mail but I have seen reports that they also use AI with their source code but the difference between Tuta Mail and Proton is that Tuta Mail hasn't pushed their devs so hard or called them losers for worrying about security issues. I think the biggest complaint right now about Proton is the fact that their CEO doesn't respect his people and is chasing money instead of taking care of the non-profit and their securty minded customers. If you're just looking for an email that just doesn't scan your stuff with AI and things like that, Port87.com might suit your needs.