Theoretically if it were already released I would say that is the niche that the framework 12 should fit in, but it is going to release in a couple of months. :/

How about Mailcow? I mean you don’t need to actually create the Mail Server in order to use Calendar. The setup is pretty straight forward

https://docs.mailcow.email/

Proton only allows port forwarding on their paid tiers, and you still need to enable it and select a server that allows port forwarding.

I would simply use something a little less fishy and cheaper AirVpn you can pair over there also with montero and some other crypto

Have been using it for quite some time now and honestly I have found almost everything I searched for and once you set the router bandwidth properly, I was capable of downloading and seeding with 2MB/s. Satisfied my needs and gotta say not worrying about Letters coming to you is very calming