Screen resolution in Boxes - strage behavior

I am using Boxes in Manjaro Gnome Since around the Update to Gnome 42 I am facing an issue with the screen resolution in the guest system.
Before, the behaviour of the boxes environment was quite convenient, the screen resolution of the host system was set automatically and usually adapted to the windows size of the Boxes window.
Since a little while, the automatic screen size setting seems not to work anymore, even when I am setting it manually there is a hickup:
My laptop’s screen size is 1980x1080, but when I select the same for the guest system the window is notably smaller (see screenshot).

The problem is the same whatever guest system I install (various Linux distros or even Windows 10).

Anybody out there with an idea, how to solve this?