This looks like the same issue as https://github.com/ValveSoftware/steam-runtime/issues/658, which is really a bug in the gamemode LD_PRELOAD module (https://github.com/FeralInteractive/gamemode/issues/347).

The Steam public beta has a workaround for this. You can opt-in to the public beta by running Steam without gamemoderun and using the GUI, or by completely exiting from Steam, echo -n publicbeta > ~/.steam/root/package/beta and running Steam again.

gamemoderun can cause other problems that can harm performance (such as repeated crashes in lsof) and there is no general workaround for those, except for not running all of Steam under gamemoderun.

For games where it makes a genuine difference to performance and does not cause crashes, you can set the launch options for individual games to gamemoderun %command% instead, to activate gamemode more selectively.

Replying to https://github.com/ValveSoftware/steam-for-linux/issues/10723#issuecomment-2050057376

Mind you, i don't have a potato pc, i made use of gamemoded just to inhibit the screensaver and DPMS. This issue made me search for a better solution and, digging on the web, i found in KDE Wayland we have indeed such a smart interface: kde-inhibit.

kde-inhibit --screenSaver --power steam

I wrote here just in case someone needs it.

@Galcian79 really offtopic here, but your case under KDE can be solved easier: create separate so called activity, disable screensaver and/or sleeping for it and run steam with games exclusively on it. When you are done, just switch back to default activity - no need to run obscure commands or close steam client launched with inhibitor.

@Galcian79 really offtopic here, but your case under KDE can be solved easier: create separate so called activity, disable screensaver and/or sleeping for it and run steam with games exclusively on it. When you are done, just switch back to default activity - no need to run obscure commands or close steam client launched with inhibitor.

I use scripts to launch games and close steam on game exit. I don't make much use of the steam client, except for managing games and browse the store. And managing env variables in shell scripts is as simple as commenting and uncommenting a line.
Anyway really off topic here.

For games where it makes a genuine difference to performance and does not cause crashes, you can set the launch options for individual games to gamemoderun %command% instead, to activate gamemode more selectively.

I'm not sure if this is an issue with the game itself, but I've found so far that doing that with SCP: Secret Laboratory causes the game to crash (no matter the Proton version) with an interesting log. This is a stretch, but perhaps this is related to the dbus NULL thing? This is also pretty recent, too.

Player.log

Interestingly, launching Steam with gamemoderun works and improves performance like before.

I'm not sure if this is an issue with the game itself, but I've found so far that doing that with SCP: Secret Laboratory causes the game to crash (no matter the Proton version) with an interesting log. This is a stretch, but perhaps this is related to the dbus NULL thing? This is also pretty recent, too.

Whether this is gamemoderun's fault (potentially the same root cause as https://github.com/FeralInteractive/gamemode/issues/347) or Steam's fault (unlikely, IMO), it's out-of-scope for this issue report, which is specifically about the "does bwrap work?" diagnostic check in steam-runtime-check-requirements.