Settings in windowed mode not working

[ppppp]

Hello,

I am using X-Plane 12.4 in windowed mode rather than fullscreen mode, to be able to use lossless scaling with a popped out window on a second screen.
However, when X-Plane runs in windowed mode, it seems not to be possible to change any settings. 
The settings window will open, but is not clickasble unfortunately (I can scroll with mouse sometimes, but thats all). Even cannot close it anymore.

Any hints would be appreciated, thanks