Look at your desktop settings. I forget where it is and I can’t find it under Catalina, I know there was a Translucent desktop setting which does this blurry effect on covered windows.
I hate the effect! With iOS it often distracts me! I have yet to find the setting in it but I have used it back in High Sierra days and it appears to be holding in Catalina.
Give this a try set your desktop image to a monochromatic color see if that changes things.