Beginning with Ubuntu 24.10, the Ubuntu on X.Org session support is now split off into its own separate package, aptly called "ubuntu-session-xsession". This is similar to what has already been pursued by Debian and other Linux distributions for splitting up the X.Org session support into a separate build. This can be useful if wanting to remove X.Org dependencies from your system or otherwise just trying to maintain a modern Wayland-minded Linux desktop without any extra legacy support or cruft. Fedora Workstation 41 for example is pursuing shipping Wayland-only GNOME desktop ISOs as their default media.
The ubuntu-session is set to recommend "ubuntu-session-xsession" and thus by default for now this Ubuntu X.Org session support will continue to be found out-of-the-box for those needing to fall-back to it on their systems or otherwise just preferring the X.Org session.
This splitting of the Ubuntu on X.Org session support into ubuntu-session-xsession was made as part of this GNOME-Session update for Ubuntu 24.10.