There are regularly unsightly white fram around some elements of the UI. I have noticed that this is related to the use of keyboard shortcuts.
I have not been able to determine exactly what key combinations cause these rectangles to appear, but I have noticed that some appear when I use keyboard shortcuts using the Shift key (for example the Ctlr Shift C shortcut to select the entire army or Shift + direction arrow when I make waypoints while moving the camera with the arrows).
Here are some screenshots illustrating this bug:
PS: I play on the Game Pass edition with Windows 10 (19043.1288)