virt-manager doesn't capture the mouse anymore: when the mouse should be
grabbed (because the guest has its own mouse pointer) if I move it too far I
see the host's pointer reappearing outside the window, but unfortunately the
two pointers don't match and I can't access all the elements on the guest's
screen.

It may be because I'm using GNOME/Wayland, I didn't check with GNOME/Xorg yet.