Huge toolbar in fullscreen

[Berlioz]

I'm running vlc on kubuntu 20.04 for some time, but suddenly my toolbar got huge. The icons stay the same size, it's just a big grey area.
I tried to drag it smaller, but it doesn't work. Also I couldn't find anything in the menus that relate to the toolbar size.
When moving the mouse around it flickers to the original size and back. It does this on all videos.
Any ideas how to get it small again all the time?

[Rémi Denis-Courmont]

Roll back the software update that caused it? Qt5 would be my best guess, but you know what you've updated, not me.

[Berlioz]

So if i understand you correctly, the problem is not with vlc at all?
That was a fast diagnosis, thanks!

[Rémi Denis-Courmont]

I guess it is not, but how would I know? I don't make VLC in Ubuntu LTS.