The weight of the flip does not cause the phone to jostle out of my grip but also fully opens it.
Pushed to prod
You're not wrong, it's just about how Proton is built right now. It's still a pretty young ecosystem.
I will menton that all of their apps (both from GP and F-Droid) work great on my OOTB Galaxy 21 and send all notifications (emails, calendar events, etc.) to my Samsung Gear 3 watch no issues.
Let's not forget that the point of Proton's services is encryption. The more points you want it to go through (Proton to Cal{SVC} to Android calendar app to watch), the more you have to relinquish that security if they aren't cooperative/companion apps.
For example, I use Proton on the web (through Tor, actually) because I get the security. If I used the Bridge, I'd be decrypting a layer just so I could use a favored email application.
Yes, you can, and I would also vouch for Nextcloud.
Anglin'