My budget gaming PC is still on Windows and RTSS is a lifesaver: I couldn't stream or record some games with my Intel Arc A580 otherwise, since titles that use DX11 or older rendering technologies typically have worse performance than the more recent ones, ergo I have to stream/record at 30 and cap the framerate anywhere between 30-60 depending on the title, otherwise things get unstable.
Of course, it's not ideal, but is at least workable. A bit odd that the card struggles with games like Ghost Recon Wildlands (DX11, 2017), but not Ghost Recon Breakpoint (Vulkan, 2019) or ones that use DX12 etc. Either that, or when there's a title that's badly coded and doesn't lock framerate properly to the screen refresh rate.
Aside from that, around 90% of the 500ish Steam games I have would actually run on Linux (various indie titles, mostly), at least according to ProtonDB: https://www.protondb.com which is pretty nice to see, except for the fact that last I checked something like GOG doesn't run on Linux natively, though thankfully something like Lutris exists.