Previous releases of Ubuntu will continue to use their previous releases of Gnome (18.04 = Gnome 28, 20.04 = Gnome 36, 21.04=Gnome 38). None will be 'upgraded' to Gnome 40.

The Ubuntu developers did not have enough testing resources or engineer time to ensure a quality experience with Gnome 40 on Ubuntu 21.04. While Gnome-shell uses version 38, most Gnome applications in 21.04 were been updated to their Gnome 40 versions.

Ubuntu 21.10 was expected to use Gnome 41, but similar resource constraints have limited the Ubuntu Desktop Team to completing the transition to Gnome 40 with some applications from Gnome 41.

You can prevent that from happening again: The Ubuntu Desktop Team welcomes volunteers to help test and fix bugs in new Gnome releases in pre-release versions of Ubuntu. (After Ubuntu release is too late.) If you want to get involved with pre-release testing, bugfixing, and integration, please dive right in. You don't need anybody's permission.