Debian has had a newer version of lightdm compared to Ubuntu since June. It appears like Debian and Ubuntu’s packages don’t have a shared history and converting it to a full merge is probably a big project. However, there are probably useful bugfixes in the new release that would be good to have in time for Ubuntu 24.04 LTS.
I heard about a LightDM issue reported to affect Ubuntu MATE. I haven’t had time to investigate it myself. Bug #2052489 “Mate Daily Graphic Layer does not come up - apparm...” : Bugs : apparmor package : Ubuntu