thanks for your answers. In general you are right: If you can connect to the same physical desktop with different users that would be even more preferable (since each user may use its own credentials). However, if we are trying this with two different users, one of the user has still to disconnect. In particular, a new window is shown whether I want to allow the connection of another user, which means that I would be disconnected. So allow me to rephrase my request:
I would like to be able that two user may connect to the same physical system seeing and interacting on the same physical screen. This is currently only possible with the workaround fra81 was posting. If I miss something here, would you please be so kind to explain to me how to enable the behavior I’m searching for?