KDE turns on do not disturb mode when a program is in full screen mode by default.
You can test this by binding DnD to a button (preferable Meta key + unused letter like F), opening a program in full screen mode and toggling DnD.
This feature can be disabled in settings.
From what I can see online the key is actually called the super key, but for some reason KDE Plasma calls it Meta on my device
Might be because I’m on a MacBook