I upgraded to F31 recently, and I now I noticed that the gnome top bar is always black. I miss the old translucent blue bar that would only go black if window was moved adjacent. I'm not sure though when this changed...
Hello Zbyszek,
I am not sure if F31 caused the problem, but as far as I know, the transparent/translucent top bar was removed from GNOME shell 3.32. You can download an extension [1] and install it using the gnome-tweak-tool to get the effect back.
[1]: https://extensions.gnome.org/extension/1708/transparent-top-bar/