fn + short cut not working anymore

Catalina 10.15.6 here

Until recently I have used fn+ keys for shortscuts. But they do not work anymore. I also a "beep"s ound if use them in BTT. Outside of BTT they just don't work anymore.

Has there been some change in macOS recently that prevented the use of fn + keys for shortcuts?

Is there some log or so visible what keyboard shortcuts arrive at BTT?
on my other mac with the same macOS fn + shortcut still work. So I want to see if some other program might interfere here (or just a OS reboot is necessary)