Forced 200 percent scaling after install on 4kuhd monitor

[Brughon]

During installation from USB Kubuntu uses 100 percent scaling with 3840x2160 resolution on my 43 inch monitor.

After installation 20.04 forces 200 percent scaling and tells me it is at 100 percent: https://ibb.co/svcdbL4

In previous editions (18.04 to 19.10) using a 2560x1440 monitor for installing and booting the first time prevented the 200 percent scaling issue. With 20.04 when I rebooted later with my 2160p monitor, scaling was back at 200 percent and settings still incorrectly said it was 100 percent.

I can imagine users with 4k screen laptops would overlook this issue.

Where do I need to report this issue?

Is there a way to force 100 percent scaling from cli?

[Brughon]

Invalid DisplaySize reported by monitor

Searching for a way to force scaling I found a hint that the monitor might not report correct DPI values via DDC: https://forum.kde.org/viewtopic.php?f=17&t=140161

I think the issue might be with the monitor. The DisplaySize is set to 162x161 dots per inch and should be 104x104 dpi.

$ xdpyinfo | grep -B2 resolution
screen #0:
dimensions:    3840x2160 pixels (602x341 millimeters)
resolution:    162x161 dots per inch

I set xrandr to use 104 dpi

xrandr --dpi 104

After reboot scaling is as expected: https://ibb.co/GCNbKC6

The commands are here: https://wiki.archlinux.org/index.php...y_size_and_DPI

[Brughon]

Part of the issue is that scaling is set based on DispalySize reported by the monitor without showing the used scaling in "Settings/Dispaly and Monitor/Display Configuration". This way the user cannot adjust the scaling if neccessary.