Steam doesn't start when launching it from app menu, but works with run command

When I try to start Steam from the app menu it gets indefinitely stuck in "loading user data" until killed from system monitor. The same doesn't happen though when i issue `flatpak run com.valvesoftware.Steam` from the terminal.

**Distribution name and version where applicable**
Debian GNU/Linux 12 (bookworm) with KDE Plasma 5.27.5

**Flatpak info**
Flatpak 1.14.4
gl drivers: default, host

These are the arguments used to launch steam from the app menu:
`run --branch=stable --arch=x86_64 --command=/app/bin/steam --file-forwarding com.valvesoftware.Steam @@u %U @@`

I tried to add these to the terminal command:
`flatpak run --branch=stable --arch=x86_64 --command=/app/bin/steam --file-forwarding com.valvesoftware.Steam @@u %U @@`
and worked fine again.

Looking in the output of the issued command I do see this:

_Steam Runtime Launch Service: starting steam-runtime-launcher-service
Steam Runtime Launch Service: steam-runtime-launcher-service is running pid 252
steam-runtime-launcher-service[252]: E: Unable to acquire bus name "com.steampowered.PressureVessel.LaunchAlongsideSteam"
Steam Runtime Launch Service: steam-runtime-launcher-service pid 252 exited
Steam Runtime Launch Service: starting steam-runtime-launcher-service
Steam Runtime Launch Service: steam-runtime-launcher-service is running pid 374
steam-runtime-launcher-service[374]: E: Unable to acquire bus name "com.steampowered.PressureVessel.LaunchAlongsideSteam"
Steam Runtime Launch Service: steam-runtime-launcher-service pid 374 exited
Steam Runtime Launch Service: starting steam-runtime-launcher-service
Steam Runtime Launch Service: steam-runtime-launcher-service is running pid 378
steam-runtime-launcher-service[378]: E: Unable to acquire bus name "com.steampowered.PressureVessel.LaunchAlongsideSteam"
Steam Runtime Launch Service: steam-runtime-launcher-service pid 378 exited
Steam Runtime Launch Service: steam-runtime-launcher-service keeps crashing on startup, disabling_

Could it be relevant?

EDIT: Adding the option "Execute in terminal" to the shortcut in the app menu shows this as well:

_nvc0_screen_create:1075 - Error allocating PGRAPH context for M2MF: -16
libGL error: glx: failed to create dri3 screen
libGL error: failed to load driver: nouveau_

There seems to be this 'nouveau' driver missing.

Start by comparing the app-menu launch arguments with the working `flatpak run com.valvesoftware.Steam` command and review the reported Steam Runtime Launch Service and nouveau errors. Done means launching Steam from the app menu no longer hangs at “loading user data” while the terminal invocation continues to work.

Written by the indexing model from the issue text.