solving grey'd out menu options

I would appreciate advice on a problem with unavailable grey'd out menu items please.
For example, I have recently installed Da Vinci 18.1 on a Macbook Pro and wish to add a larger external screen to view the timeline on. When I go to Workspace - Dual screen, the On and Fullscreen timeline options are both grey'd out and inaccessable. Is it a fault within the programme, or am I missing something essential in my setup. Advice on how to correct this and similar grey'd out options would be much appreciated.
thankyou. Phil Dadson / New Zealand

[Peter Chamberlain]

Greyed out menus mean they are not available in that page or some other config prevents it.

check your mac system settings for the monitor config

Make sure they are set to extended and not to mirrored. And then, you need to restart DR.