These are just my thoughts, and it’s possible I may have mixed the mark, so I apologize if I’m wrong.
I suspect here you are logging in, but don’t recognize that you’re logged in. When I login I get a black background and cursor; which is what I expect. On right click of black background I get the openbox menu, ie. a simple openbox session. Selecting ‘exit’ in the menu asks for confirmation of ending the openbox session and logs me out when I click Exit.
I suspect this is what you have, but that you expected more (it’s like a clean slate that you can turn into whatever you want, but it’s pretty bare by default).
I do recall situations where the background didn’t blacken (so it looked like you were still on the sddm greeter screen) but I didn’t find the bug reports for those on launchpad and there were old so likely no longer apply.
Yes some decisions made by Ubuntu have slowed my boot times for Lubuntu (snaps come to mind), but I’ve learnt to be patient as there are benefits with snaps, and not waiting creates more issues for me with chromium (the browser I use for this and a few Ubuntu sites) so I adjusted my behavior & wait until a notification appears top right as a clue the system is ready.
It’s also possible changes made to our systems slow the startup down to; me I’m happy with this as I don’t logout/login multiple times a day as I don’t work in a office where I get called away constantly. I can’t really help here though.