Since the latest Proton Experimental almost all games open on the wrong monitor in a multimonitor setup

[MarcusSchwarz]

Heya, I have a multi-monitor setup. The main monitor is in landscape mode in GNOME as monitor 1, and a second monitor to my left is in portrait mode, defined as monitor 2. It seems to me that since the last update of Proton Experimental, almost all games now open on the second monitor instead of the main monitor. If I switch to an older stable Proton version like 10.4, everything works fine again. With Proton 11 beta, I have the same problem as with Proton Experimental.

This behavior can be reproduced with many games, here are a few:
Proverbs, App-ID: 3083300
Chillquarium, App-ID: 2276930
The best Duck clicker, App-ID: 3110500
Forage Wizard, App-ID: 3868320

Breaking Proton versions:
=== Installierte Proton-Versionen ===
- Proton 11.0 | version: 1779182095 proton-11.0-1-beta5 | buildid: 23302971
- Proton Hotfix | version: 1779092246 hotfix-20260518-fh6 | buildid: 23283288
- Proton Experimental | version: n/a | buildid: 23289363

Working Proton version:
- Proton 10.0 | version: 1769167055 proton-10.0-4 | buildid: 21617411

General system info

=== Kernel ===
7.0.3-1-MANJARO

=== CPU ===
AMD Ryzen 7 5800X 8-Core Processor

=== Grafikkarte ===
07:00.0 VGA compatible controller: NVIDIA Corporation AD104 [GeForce RTX 4070] (rev a1)

=== GPU Treiber ===
OpenGL vendor string: NVIDIA Corporation
OpenGL renderer string: NVIDIA GeForce RTX 4070/PCIe/SSE2
OpenGL version string: 4.6.0 NVIDIA 595.71.05

=== Vulkan ===
GPU0:
	apiVersion         = 1.4.329
	driverVersion      = 595.71.5.0
	deviceType         = PHYSICAL_DEVICE_TYPE_DISCRETE_GPU

=== GNOME ===
GNOME Shell 50.1

=== Distribution ===
NAME="Manjaro Linux"

=== Steam Runtime ===
steam-runtime_1.0.20260316.216267

=== Display Server ===
wayland

=== Monitore & Auflösungen ===
interface: 'wl_output',                                  version:  4, name:  5
	name: DP-1
	description: LG Electronics 27"
	x: 1440, y: 635, scale: 2,
	physical_width: 600 mm, physical_height: 340 mm,
	make: 'GSM', model: 'LG HDR 4K',
--
interface: 'wl_output',                                  version:  4, name:  6
	name: DP-3
	description: LG Electronics 27"
	x: 0, y: 0, scale: 2,
	physical_width: 600 mm, physical_height: 340 mm,
	make: 'GSM', model: 'LG HDR 4K',
DP-1 connected primary 5120x2880+2880+1270 (normal left inverted right x axis y axis) 600mm x 340mm
DP-3 connected 2880x5120+0+0 left (normal left inverted right x axis y axis) 600mm x 340mm

[Renari]

This is a gnome issue, there's nothing that can be done here.

ValveSoftware/steam-for-linux#7205 same issue, maybe there's some workarounds there.