Your system information

• Steam client version (build number or date): 1719967667
• Distribution (e.g. Ubuntu): CachyOS Linux 6.6 LTS with Plasma 6.1.2
• Opted into Steam client beta?: Yes
• Have you checked for system updates?: Yes
• Steam Logs: steam-logs.tar.gz
• GPU: AMD 6700 XT

Please describe your issue in as much detail as possible:

When I loaded up Elden Ring to see how it looked in HDR I was level 20 instead of 78 and not outside of the boss room. I investigated the differences between my desktop and the Steam session provided by ChimeraOS and the -steamdeck parameter was the culprit. I assume Steam synced with an old game save when it created the new compatdata and synced with the cloud. Fortunately my save game was intact in the compatdata on the external drive so my game wasn't lost.

I only caught this because I use the ChimeraOS Steam session to play games on Linux in HDR and Steam synced an older save instead of my latest save. My controllers aren't detected when I launch games with "gamescope -- %command%" so I have to use Steam BPM sessions for HDR gaming. The Chimera OS session makes it easy to get a Steam BPM session up and running on Linux with minimal effort.

Just using that flag with the desktop client is enough to trigger the compatdata to be created on $HOME instead of using the existing data on the external drive. Nothing related to ChimeraOS causes the issue.

Steps for reproducing this issue:

1. On a desktop, launch Steam and start any Proton game that's stored on an external drive. If that game has never been ran the compatdata will be stored on the external drive along with shaders, etc like it always has.
2. Launch Steam with the -steamdeck launch parameter and run the same game. Instead of using the previously created compatdata on the external drive it'll treat launching the game as the first time running it and create a new compatdata under the default Steam location on $HOME.