It's only CPUs lacking a specific extension. Nehalem or newer for Intel or Phenom or newer for AMD will still work. Those CPUs aren't even officially supported by their weird restrictions.
So this is anecdotal I know, but I work on a Mac, so I've only ever held on to Windows for gaming. (Sidenote: The Mac isn't my choice, either, but it has a terminal, and it does the job)
I've definitely tried to go fully Linux in the past, but it was always gaming that killed it for me. Wine was just never very consistent for me in this area.
Long story but, I recently lost my gaming machine, and was gifted a friends old one. Also a long story, but he ended up putting Linux on it for me. I figured I'd use it as is until payday before buying a key for Windows.
Holy shit gaming on Linux become has easy! Steam/proton is amazing!
I won't lie, it's not always as simple as install and run, but the tweaking that's been required has been orders of magnitude simpler than what it used to be. Click a box 90% of the time, Click a box and add a run parameter for another 5%.
The only games that haven't worked for me are Starfield and Cyberpunk (accounting for the last 5%.)
Starfield might just be too much for this old machine, but Cyberpunk I have no idea. Neither are a huge loss to me when Balders Gate, and Elite Dangerous are running fine. Also long standing favourites like Just Cause 3/4 work perfectly too.
I'm thrilled and a little shocked to say I think I'm finally done with Windows
I installed in dual boot configuration save for the fact that I haven't yet booted back into Windows since.
Generally my games just work. More than that, the performance is great and the tweaks are few and far between where necessary. It's an absolute world of difference in usability compared to a few years ago.
Do it. I made the switch a few months ago, and it's gone better than I'd expected. Now running Linux Mint on my desktop and laptop. I set my laptop up with dual boot, just so I can easily and natively run Windows apps if needed.
I'd recommend everyone switch to Linux! I only had to go back because of a very niche problem with head tracking support. Linux is ready for most people though.
Freetrack in my simulation games is why I still have Windows on my old gaming desktop - the tracking protocol that those sims use isn't supported under Linux 😔 as well as another that specifically looks for the Logitech G hub to interface with the wheel.
Aside from the simulators, I've been gaming on Linux on my deck and haven't run into any issues at all, especially with Proton-GE handy to run "unsupported" titles