Comment 3 for bug 2019983

Intel® HD Graphics 4600 (HSW GT2)

But I think I found my mistake :

I had added to my /etc/environment

MESA_LOADER_DRIVER_OVERRIDE=i965

Since I removed some things work better :

⋅ the gear icon show up on login screen ;
⋅ windows and gnome-shell animations are back

but, there's always a but, first launch of Firefox leads to a black window,
probably related to https://bugzilla.mozilla.org/show_bug.cgi?id=1828161

tl;dr

in Ubuntu 23.04 don't add MESA_LOADER_DRIVER_OVERRIDE=i965 to /etc/environment