You did say "I'd like this to be the end of my Windows usage." Even so, if you're not ready to move tomorrow, you can give up some privacy for the next year and continue to get patches by logging in to Microsoft. Windows 10 LTSC is a possibility if you somehow qualify for a license, although there's no guarantee the latest Nvidia drivers will work on it, some version of them will, or you can punt and run Linux on your current PC until the steam cube comes out. Pick a Linux distribution you like and run Steam, or go down the rabbit hole of running native Steam OS.

I personally preferred Fedora for this but mostly because my employer is a redhat shop. It's not otherwise (as far as I know) any better or worse than any other distro for gaming.

I game exclusively on my Linux desktop (for the few games I play). Everything works flawlessly with Proton.