I have a 1440p and a 2160p monitor connected to the same system. I want to scale them so that applications are approximately the same size, hence choose scale factors of 140% and 200%, respectively. I let legacy applications (X11) apply scaling themselves as this nice feature was recently introduced. If I then try to play a game on Steam, the game (and Steam itself) believes my resolution to be approximately ACTUAL_MONTIOR_RESOLUTION * SCALING_FACTOR, so on my 1440p monitor the games believe they are running on a screen of dimensions 3656x2060 which is almost 1,4 * (2560x1440) = 3584x2016. 

I think this behavior should not be desired due to some games not running well when using a lower target resolution than believed monitor resolution and due to things like the Steam interface not scaling properly due to believing the resolution to be different than it is. Also, by turning off a single monitor the problem resolves itself with xwayland-applications believing the resolution to be what it actually is. Many other applications such as Firefox and others are scaling fine though. Games outside of Steam experience the same issue.

STEPS TO REPRODUCE
1. Apply scaling with different scaling factors on a setup with multiple monitors using wayland, leaving the X11-applications the option to scale themselves.
2. Open an xwayland application that allows using different resolutions, say a game.
3. The application believes the resolution is higher than it is (assuming a scaling factor greater than 1 on both monitors) thus needing to adjust settings if possible to ensure not rendering in higher resolution than what will be displayed.

OBSERVED RESULT

Xwayland applications believe the resolution to be different than what it actually is.

EXPECTED RESULT

Xwayland applications believe the resolution is the one that it actually is, such as in the case of only one monitor connected.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 6.0.2-arch1-1 (64-bit)
KDE Plasma Version: 5.26.1
KDE Frameworks Version: 5.99.0
Qt Version: 5.15.6

ADDITIONAL INFORMATION
Graphics Platform: Wayland