I think the current configuration is to not control the logged in screen, but to log in a new session. And when that happens, your current one gets signed out. Not sure though, last I tried VNC on linux (like 6 or more years ago), I was getting a new session with the same user.
Not sure what I can advise. Try to set the VNC server as a service in systemd? Or maybe switch to x2go, Jay did a video on it (probably skip around min 10).
There is an x2go client for windows.