To anyone reading this thinking "once SteamOS comes out, I'll switch", you should know:

Gaming on Linux is already here. Pick a distro and game. You can take advantage of Proton right now. You don't need to wait for one specific distro.

I've personally been gaming on Linux exclusively for about 3 years. Windows games, not Linux games.

Edit: based on other commenters' suggestions, I'll give you some.

I have gamed for those three years on PopOS. It is a distro based on Debian, ultimately, which means it's also related to Ubuntu and Mint. Realistically, you can pick any of those 4 and you should have a nice experience.

Arch is popular with the übergeeks, and I do use it on my laptop, BTW, but you shouldn't use it as a first distro.

The concept of "distro" doesn't really exist for Windows, because you pretty much get one monolithic product. But basically, it is a specific mix of software that works together and relies on the Linux kernel. Imagine it as a "version" of Windows with specific goals, some of which are overlapping (e.g. Mint and Ubuntu tend to cater to the same audience).

If you get far enough into it, the freedom that Linux allows means that you can turn any distro into any other distro.