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.