Problem with night color mode in x11, kde plasma

Hi,

I have upgraded my Kubuntu from version 22.04 LTS to version 24.04 LTS and I am using nouveau as graphics driver, because I am using a graphics card by NVidia. When I am using x11, I assume, that the night color mode has a bug, because it’s switching back and forth between two color temperatures every few seconds. It doesn’t matter, whether night color mode is enabled or disabled. I have tried the proprietary driver by NVidia instead of nouveau, but the problem was still there.
The former Kubuntu version that I used (22.04 LTS) worked properly with x11, nouveau and night color mode.
When I use Wayland in my current Kubuntu version, the night color mode also works properly with nouveau, but the problem is here, that my system is crashing constantly in Wayland, when I use my browser (Brave browser) in combination with Thunderbird opened. And I am using my browser and Thunderbird both opened at the same time a lot, so the crashing of my system in Wayland is annoying, too. That is why I want to use x11 again.
Can anyone help me or tell me, if I should report the night color problem in x11 as a bug in the KDE bugtracking system? Because I am not sure, if this is really a bug.

Thank you very much and best regards,

Vin