They have some shady (or at least questionable) enough actions in their past, some even covered by mainstream media, that made me dismiss them as an option. I went with the German hosted mailbox.org instead. Swiss law (where proton is hosted) is actually quite a bit less protective of privacy than EU/German law, or maybe just protected in other ways. The international reputation of privacy protecting character of Swiss law seems to be outdated?

Just to be clear, I can't remember exactly what the specific events were that caused me to reconsider back when I switched years ago. When I just did some quick (!) searches just now, I found statements that they would only record ip addresses in "extreme criminal cases", but examples include cases of trespassing and property damage. Not exactly child molesters and serial killers (example source). I also understand that the (Swiss) laws relevant to them probably forced them to, but at the very least that seems dishonest or misleading advertising.