sharing screen
how to share a my 2017 27 in screen with a iMac new
how to share a my 2017 27 in screen with a iMac new
If you mean Target Display Mode, that has been dead since 2014.
However if you mean actually screen sharing please refer to Share the screen of another Mac - Apple Support . If you still cannot get it to work after using the Screen Sharing link info please give AppleCare a call. AppleCare Contact Info
sharing screen