19,1 iMac 10.15.3, Thunderbolt 3 /Thunderbolt 2 Apple adapter+Thunderbolt 2 cable to 17,1 iMac 10.15.3. I just want to extend my 19,1 monitor onto the 17,1 monitor, and I need Arrangements to show in System Preferences/Display window, but it is not there on either iMac. I have no trouble screen...