Question about screen resolution in plasma 5 using x11 and a 4 K monitor arrangement.

[Stakanov]

Hello 

I have a AMD Radeon Pro WX5500 Graphics card (5xDP 8GB Ram). 
My monitor is a Lenovo P32p-20.
Plasma runs opensuse TW in dual mode with X11 (as Wayland with dual monitor 
support does not work in multi user environment. 

Although the native resolution is 3840x2160 at 60 Hz, the offered resolution 
is only 2560x1440 at 75 or 60 hz. 

Obviously the problem is not the graphics card, nor the monitor and the 
monitor is branched with DP on DP. 
The other monitor is a smaller Medion MD20666 which runs with 60 Hz on its 
native resolution (1920x1080). 

It came to my mind that maybe the Plasma desktop cannot be resolved over the 
proposed 2160x1140. 

Could you tell me if plasma has a resolution limit and maybe cannot fully 
resolve 4K? This would help me very much. 

Thank you in advance.