Transperant menus: how to disable?

Hello,

for some reason pull down menus and right button menus are transparent now on my machine. I did not change anything in KDE systemsettings, I did not install new themes, I did not change windows appearance. I have no idea why those menus are transparent now, they were not transparent yesterday. But yesterday some updates have been installed. Could this be the reason for this mystery?

“KDE systemsetting → Window Management → Window Rules” is NOT activated, and it has not been activated for months.

Is there any other place where transparency is defined or set? I really need to switch off transparent menus, they are very hard to read.

My system:

Operating System: KDE neon 6.0
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0
Kernel Version: 6.6.30 (64-bit)
Graphics Platform: X11

Chosen desktop theme: Breeze Dark