Mussar
Mussar
I am having similar issues with opacity, regardless of the decorations settings:   
Selecting English in the language menu only fixed the XCA GUI, and the language remained in Indonesian when navigating through the Finder sub-windows. the plist fix @iMunas posted fixed that...
I'll also update mine and start including those in the completions I have in queue.
Unfortunately, does not seem to change the behavior @nounderline.
I was also able to reproduce this on an M1 Mac Studio @ os 15.5, @cakebaker's fix worked.