Second screen makes all task bar icons disappear and window font is changed [KDE Plasma]

Whenever I set my second screen to “Extend Right”, dragging any window into it makes it change the font of its titlebar and passing the mouse over any app icon in the titlebar (opened window or tray) makes it disappear (except for the keyboard, arrow for more and a few others).

Logging off fixes it until I redo “Extend Right”.

NB: This is with, when I try with Wayland the screen isn’t recognised

Titlebar with the changed font

Taskbar with no icons

Where do you do that?
From you previous topics i gather you have some Nvidia GPU and you made use of nvidia-xconfig that creates the /etc/X11/xorg.conf that conflicts with /etc/X11/mhwd.d/nvidia.conf

Is the same if you apply whatever new setting from Nvidia X Server Settings and the KDE Plasma Settings > Display and Monitor > Display Configuration has a different layout. On System Settings you only have to drag the monitor you want in the position you want (that when using the default, dynamic layout used in the default /etc/X11/mhwd.d/nvidia.conf).

If you previously had manually added a fixed layout in /etc/X11/mhwd.d/nvidia.conf when changing the arrangement in Nvidia X Server Settings and apply, it will conflict with the information Xorg provided from the config, making then the KDE Plasma Display Configuration to act up.

~/.cache/ is becoming an issue in some of such circumstances too.

Extend right is an option from the screen menu opened with Win+P (or Fn+F10 on my laptop)

I have better diagnostic now : when I reboot my computer in that mode, it triggers the issues I presented above; when I go to sleep and resume, I have other errors.

I didn’t edit any of those files manually, the worst I did was run a command/program.
Both /etc/X11/mhwd.d/nvidia.conf and /etc/X11/xorg.conf.d/90-mhwd.conf are empty (they only have a “generated by mhwd” comment).
I don’t know where to look in .cache for problematic files

I finally found a temporary solution that doesn’t involve downgrading all plasma packages to 5.24.X. You just need to downgrade kscreen and libkscreen to 5.25.1. You need to install downgrade.

sudo DOWNGRADE_FROM_ALA=1 downgrade kscreen libkscreen

Please be careful about this though. Not sure of the long-term (or even short-term) problems of having kscreen and libkscreen lag behind in updates.

Can you explain what the underlying issue is ?