I verified that this regression also shows in Fedora 37. I verified there because Fedora and Ubuntu ship a patch to enable transparency in gnome-terminal; gnome-terminal upstream does not have that feature.
I also verified that this regression was introduced in mutter 43.1. (transparency works in 43.0 but not in 43.1).
With that information, I found an upstream bug report. The initial response was that the new behavior conforms to the specification and it was suggested to maximize gnome-terminal instead of using fullscreen mode if you want this feature.
I verified that this regression also shows in Fedora 37. I verified there because Fedora and Ubuntu ship a patch to enable transparency in gnome-terminal; gnome-terminal upstream does not have that feature.
I also verified that this regression was introduced in mutter 43.1. (transparency works in 43.0 but not in 43.1).
With that information, I found an upstream bug report. The initial response was that the new behavior conforms to the specification and it was suggested to maximize gnome-terminal instead of using fullscreen mode if you want this feature.