Valve’s use-case for choosing a gnu+linux distro is likely to be different from yours. Therefore, commentary about Valve’s needs and choices may or may not be relevant to your use-case.

If you’re new, I recommend mint. Because of ubuntu’s questionable choices at times vs debian’s steady hand, I recommend the debian edition of mint, LMDE. It’s a rolling distribution that requires fewer total reinstalls. Debian’s low-effort stability and security works for nearly all use-cases. Mint adds user-friendly settings, updates, and package management.

Cinnamon is mint’s desktop environment, what they add on top of ubuntu or debian. Like xfce, it’s lighter-weight and more responsive than plasma or gnome on lower-end or aging hardware, but it’s prettier than xfce without rice. Although if you wanna rice and make it pretty, check out a tiling window manager.

Let Valve handle the complex stuff and hire employees to stress-test the latest packages in Arch and just use what they package for you in proton. Start with a debian derivative. If you start wanting to tinker around because you’re getting comfortable, or for some reason desperately need a newer version of a package, you can try software from other package management schemes like guix or flatpak that run on top of your stable debian system.

When you’re comfortable with using the command line tools and managing the gnu operating system, you can try a more command-line centered and manually assisted distros like arch and gentoo