Blender even crashes now with a segmentation fault – core dump …
I think you are right, I will bug report it.
Mh … I must haved activated Overlay Next some time ago,
Iliya Katueshenock made me aware of it.
The problem I described could be fixed by disabling Overlay Next!
Looking into the project, it seems very basic at the moment. I guess it was my error that I activated it pre-mature. Now Overlay Next is disabled, and everything works fine on my cute little celeron.