Steam client version:
1782861641 (SteamClient023)

SteamOS version:
Steam Deck Stable

Opted into Steam client beta?:
No

Opted into SteamOS beta?:
No

Have you checked for updates in Settings > System?:
Yes

Additional system information:
KDE Plasma: 6.4.3
Kernel: 6.16.12-valve24-1-neptune-616-gc748040e4712 (64-bit)
Graphics Platform: Wayland
CPU: AMD Ryzen 7 7800X3D
GPU: AMD Radeon RX 9060 XT
RAM: 32 GiB
Motherboard: ASRock B650M Pro RS WiFi

Please describe your issue in as much detail as possible:

In Desktop Mode, I have "Start Steam in Big Picture Mode" disabled in Steam's Interface settings. Despite this option being turned off, Steam continues to launch directly into Big Picture Mode every time it starts.

Expected behavior:
When "Start Steam in Big Picture Mode" is disabled, Steam should launch using the standard desktop interface.

Actual behavior:
Steam ignores the setting and always launches in Big Picture Mode.

This appears to make the setting non-functional in Desktop Mode. For users who use SteamOS as a general-purpose desktop operating system in addition to gaming, having Steam automatically open in the standard desktop interface is important for productivity and general desktop use.

Steps for reproducing this issue:

1. Boot into SteamOS and switch to Desktop Mode.
2. Open Steam and disable "Start Steam in Big Picture Mode" under Settings → Interface.
3. Exit Steam completely.
4. Launch Steam again (or reboot the system and allow Steam to start automatically).
5. Observe that Steam still launches in Big Picture Mode instead of the standard desktop interface.