If you can’t share Mac computer screens
If you’re having problems sharing your screen with another Mac or viewing a shared screen on your Mac, there are several things to check.
Make sure you turned on screen sharing or remote management and set up sharing permissions on the Mac whose screen you want to share. See Turn Mac screen sharing on or off.
If you’re trying to share the screen of another Mac, on that Mac choose Apple menu > System Preferences, then click Sharing and make sure you’re in the list of users who have permission to share its screen.
Make sure neither Mac is in sleep mode. If necessary, adjust sleep settings using Energy Saver preferences (choose Apple menu > System Preferences, then click Energy Saver).
Make sure both computers are connected to the same network.
To check your connection, choose Apple menu > System Preferences, then click Network. The indicator next to your type of network connection should be green. For a Wi-Fi connection, the network name is displayed in the pane on the right.