I agree with a bunch of the comments here but wanted to add that there’s a decades-long legacy of good FOSS/Linux support on Thinkpads. Before any of these companies existed, Linux was running pretty reliably on Thinkpads.

I do like the newer options with these newer manufacturers, but I won’t be getting rid of my Thinkpads any time soon. I’m running a Framework now too.

How does the immutability come into play with Nitrux vs, say NixOS?

I’ve read that systemd-homed can do encrypted home directories but I haven’t tried it, much less on WSL but that may get you to achieve the encrypted home directory at least.

Personally I don’t think I would have a need to encrypt all of WSL, but maybe that also makes sense for your case.

ArchWiki example: https://wiki.archlinux.org/title/Systemd-homed

I’ve used Arch, Manjaro, and Endeavour. For ease of use it’s between Manjaro and Endeavour and I’d pick Endeavour. Arch is great too. When you’re ready to go deeper, give it a shot.