SUMMARY

When adding filter layer (in Ubuntu), the settings window is obscuring large part of the image and can't be moved, as it's "attached" to the main window. Also the image under the window get's dimmed, so the usage and preview of any adjustement filter, like levels or color correction is pointless, as you don't see what you are really doing. 

STEPS TO REPRODUCE
1. Add filter layer in Ubuntu


OBSERVED RESULT

Filter window obscuring and dimming the image.

EXPECTED RESULT


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Ubuntu 20.04, Gnome 3.36.8
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION