Steam Running Under Gamescope w/ MangoHud Overrides User-set MangoHud Configurations

[ThisNekoGuy]

Describe the bug

When using mangohud in conjunction with gamscope to run Steam itself, games subsequently launched don't respect the user configuration set by goverlay (it forces its own preset for some reason). I had made an issue about this to Valve, here:

• https://github.com/ValveSoftware/steam-for-linux/issues/11879#issuecomment-2778382178

but they insisted that I approach mangohud about this issue first (despite that it only affects Steam).

List relevant hardware/software information

• Linux Distribution: Gentoo (LLVM)
• MangoHud version: v0.8.1-28-g2a93809+ (mangohud --version)
• GPU: AMD RX 7800 XT

To Reproduce Steps to reproduce the behavior:

1. Change the mangohud configuration to something like the "FPS Only" preset (the specifics shouldn't matter, but it's what I did)
2. Run Steam though gamescope (I used Big Picture Mode and enabled the gamescope -e flag to avoid bugs with the BPM Steam overlay) and enable mangohud
3. Launch a game through Proton

Expected behavior

MangoHud's display configuration should be respected, but it's overridden by Steam.

[flightlessmango]

When gamescope is in "steamMode" it will create a temporary config file and set MANGOHUD_CONFIGFILE to that file. This is intentional for steam deck etc. I think this is the cause of the issue. I would recommend creating an issue on gamescope git