Your system information

• Steam client version (build number or date): 1709920887
• Distribution (e.g. Ubuntu): Arch Linux
• Opted into Steam client beta?: Yes
• Have you checked for system updates?: Yes
• Steam Logs: (Can provide on request)
• GPU: AMD
• Desktop: KDE Plasma 6.0.1, X11

Please describe your issue in as much detail as possible:

I need to set STEAM_FORCE_DESKTOPUI_SCALING=2.0 for steam to be usable in my 4k display, I also set scaling to 200% in KDE Plasma system setting.

On launch steam respects the 2.0, but when entering and exiting Steam big picture additional scaling is applied making steam scale 4.0.

Not setting the environment variable will make steam UI start scaled to 1.0 until entering and exiting Steam big picture were it will then be 2.0.

Entering and exiting steam big picture does keep doubling the scaling, it will stay at 4.0

This does not happen in Wayland session, where scaling will stay at 2.0.

Steam should not re-double the scaling after exiting big picture, Ideally steam should also pickup system set scaling without needing an environment variable.

Steps for reproducing this issue:

1. Start a X11 KDE Plasma session
2. Launch steam with STEAM_FORCE_DESKTOPUI_SCALING=2.0
3. Enter and exit steam big picture mode