The source project of this merge request has been removed.
ubuntu: Enable express install for 18.10 and 21.10
With these changes, Ubuntu Express Install worked for me with GNOME Boxes 42 for Ubuntu 18.04 LTS (already enabled), 19.04 (already enabled), 18.10, 21.10, and the current daily 22.04.
For other releases, I ran into https://gitlab.gnome.org/GNOME/gnome-boxes/-/issues/779