QGIS display issues: buttons, menus, ... unreadable

Under my system with Ubuntu 24.04, QGIS is unusable because of cropped buttons, menus that cannot be read, text that is not properly displayed everywhere. You can see an illustration here:

Image may be NSFW.
Clik here to view.

I use the window manager AwesomeWM. But maybe it is more an issue related to QT?I tried with QGIS stable version and also the Grenoble version. I installed QGIS using APT and also flatpak. The problem is always exactly the same.

(QGIS was working fine under Ubuntu 20.04 which I was using before, with a similar configuration under AwesomeWM, etc.)

Thanks for any hint...