New UI update breaks scaling

**Problem description**

So apparently:

> Steam will now use the system's global scale factor as configured in KDE settings. Specifically org.gnome.desktop.interface/text-scaling-factor.
> Added a commandline switch to override the window scaling factor: "-forcedesktopscaling ".
> Dynamically update the UI's scaling factor when the KDE system scaling setting changes.

The issue is, it doesn't work.
I've tried to set the desktop-scaling manually, but it doesn't change anything.
my text-scaling-factor is set to 1.5 however, the Steam interface is still running at 1 (apparently) making everything too small.
I've also tried to set it to 2 to see if this fixes the problem, but it doesn't. It looks like it doesn't read the variable at all(?)
How can I fix this? With the old UI it was scaling to 2 I think, as it was bigger than normal, but still usable.

**System info:**
OS: openSUSE Tumbleweed x86_64
VERSION="20230613"
Kernel: 6.3.7-1-default
Resolution: 3840x2160 @ 32-inch 16:9 monitor
DE: GNOME 44.2
WM: Mutter

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

**Does this issue reproduce with native Steam**
Have not tested

Start by reproducing the issue in the Flatpak on GNOME with text-scaling-factor set to 1.5 and 2, then compare the result with native Steam as suggested in the report. Check whether the -forcedesktopscaling override changes the UI size; done means the configured desktop scale and command-line override affect the interface as expected.

Written by the indexing model from the issue text.