

A lot of people would suggest GNU/Linux as operating system, my suggestion is FreeBSD.
- It runs rock solid.
- It runs on a lot of platforms. Architectures
- There is only one FreeBSD and not a hundred of distros.
- It has a very good BHYVE (virtual machine) and Jails architecture.
- One can run Linux Apps (no emulation!) within FreeBSD.
- There are a lot of applications, which you can find at FreshPorts, explained at one place and the possibility to contact the port manager.
- A lot of desktop environments and window managers. e.g. WindowMaker, what can be very slim and usable.
- It is very well documented: FreeBSD Handbook
Just my 5 (8)Cents. ;)
In my opinion, Tutanota https://tutanota.com/ is a better choice than Proton, there are apps for Linux, Windows, macOS, Android iPhone, working nicely together.