What command will launch lubuntu-desktop 20.04?
startlxqt
From man startlxqt
startlxqt is a shell script meant to initialize and launch LXQt sessions. It is as such similar to counterparts of other desktop environments like startlxde in LXDE or startkde in KDE. It's main tasks are exporting environment variables, partly after performing corresponding checks, and launching lxqt-session, the LXQt session manager. It is not meant to be run by users. Rather, it is invoked as backend, e. g. by script startx on virtual terminals or display managers like SDDM or LightDM, see section EXAMPLE.
Note: I QA-test & use Lubuntu/LXQt only locally, so I've not tested this via VPN/vnc/remotely. This is the LXQt equivalent command to your listed examples in the question.