How to setup persistent vnc sessions for various users via the command line only?

Hi.
I seem not to be able to find other documentation on setting up vnc session than this:

Unfortunately, this does not help in my scenario: The machine sits “behind bars” in a in a rack in a computing center. The machine is only reachable by ssh. So vnc has to be tunneled through ssh, no other port to the outside is open.

I managed to run yast in the shell to enable the persistant sessions. However, running remmina eventually fails saying the vnc session is closed. The debugging tells that the ssh tunnel is established and vnc parameters are exchanged but then “polling the tunnel” fails. I assume there is just nothing to connect to.

Because: How could it? There is no graphical desktop that I can log in to to share this desktop via “persistant” vnc as explained in the above documentation. In a way, the desktops needs to start automatically after booting and users connect to their own desktop. Under centos8stream (cough) tigervnc was instructed to reserve a display number for a named user.

Here, with opensuse leap-15.6, I do not even know, if it is tigervnc that provides the desktop. And it needs to be instructed to provide the vnc ports only locally for the ssh tunnel to pick them up.

I’d be very grateful for pointers or instructions.

Many thanks.

PS: The onetime sessions are no option as computations may run for days or even weeks. One needs to be able to disconnect and reconnect at times to the same vnc desktop with its continuously running programs.