I keep running into internal self-test errors, e.g. if I use Free-form input and type
"= caffeine molecule" and then click on the + to show all results.
The scrollbar starts vibrating and the notebook is completely stuck. Sometimes it throws an internal self-test error with the file DXScreenGraphics.cpp.
I'm running Mathematica 12.3 on Windows 10.
I am on Windows 10 as well and also have this problem on Mathematica 12.3 with Free-form Input / Show all results
Unlike you Andreas I don't get any Internal self-test errors. But as you say the front end becomes stuck. Cannot abort evaluation, close the notebook, start a new cell or do any other action. Only way out is to kill Mathematica through the Task Manager.
There is no problem on Mathematica 12.2