I dont see anything in your post that isnt already possible on Linux. OBS and GPU-Screen-Recorder both work great, I dont know what features could be needed that they dont offer.
Gamescope is capable of upscaling games with FSR. It doesnt support as many upscaling options as Magpie, but clearly the capability is there and not restricted by anything inherent to Linux.
I dont see anything in your post that isnt already possible on Linux. OBS and GPU-Screen-Recorder both work great, I dont know what features could be needed that they dont offer.
Gamescope is capable of upscaling games with FSR. It doesnt support as many upscaling options as Magpie, but clearly the capability is there and not restricted by anything inherent to Linux.