Can't mirror MacBook Pro
When connecting my MacBook Pro to an external monitor or projector, it wont let me mirror displays. When I check the 'mirror displays' box it immediately switches back to extended display. This happens on every external monitor/projector I have tried. MacBook Pro 13" retina 2017 (4 Thunderbolt 3/USB-C ports). Currently on OSX 10.15, was the same on 10.14.
MacBook Pro Retina