I should mention, all testing was done in Manjaro Linux and using the steam-manjaro package on the Host device. I have not confirmed this behavior with the steam-native package, or on any Linux distribution other than Manjaro.
I can confirm this happening on my PC too.
I checked that this bug still exists.
Still a thing. The screenshot sound is heard but nothing is saved on neither the host or the guest computer.
Nothing extracted yet.
OS: Manjaro Linux
Client: steam-manjaro
Proton: Any version (tested in 4.11 and up)
Host DE: KDE Plasma
Screenshot functionality seems to be disabled/broken when running games under Proton and streaming via Remote Play.
Screenshot Hotkeys/Chords function as expected under Proton when Remote Play is inactive, and in native Linux games with our without Remote Play, but are unresponsive when Proton and Remote Play are used in combination.
I have confirmed negative results with two games running under Proton (FFXIV and Cuphead), and positive results with two linux-native games (Rise of the Tomb Raider and Hyper Light Drifter).
Testing was done in multiple Proton versions going back to 4.11, and Streaming to a variety of clients including both Linux and Windows desktop clients, Steam Link hardware, and Steam Link for Android, all with consistent negative results.