Under “Connection” the “Port” field contents are shown in grey when “Display Number” is set to “Auto” suggesting that the value cannot be altered - which in that case it should be so - yet it can be altered. I appreciate the “Display Number” is changed accordingly when the value is altered but it’s shabby.
The option “Keep existing viewer if a new viewer tries to connect” under “Sharing” is a dependant of “Allow only one VNC connection at a time”. This relationship breaks down when one selects the controlling parameter and sets the dependant followed by selection of a different controlling one - i.e. the dependant stays set.