Just in general: More sane defaults, less RTFM. Sure, you can configure everything, but MUST you? A lot of opensource developers seem to believe that configurability is a get-out-of-jail-free card for having to provide a good user experience out of the box.
Proton seems on the wrong side of the usability - privacy spectrum. Every last feature I’d want from an online provider is impossible or massively neutered by the overly strict security.
I wish there was a similar service in a trustworthy country with a more sane level of safety, like opt-in encryption for example.