Click the Library pop-up menu in the toolbar, then choose Both Libraries or Shared Library.
To view sharing suggestions, click For Your Shared Library in the sidebar.
Do one of the following:
Move a selection of items: Select the items you want added to the Shared Library, Control-click one of the items, then choose Move [number] Photos to Shared Library.
Move all suggested items: Click Move All to Shared Library at the top right.
To get sharing suggestions for additional people, choose Photos > Settings, click Shared Library, then click Add Other People. Select people you want to include in sharing suggestions, then click Add. To remove someone from sharing suggestions, hold the pointer over the person’s photo, then click Set up or join an iCloud Shared Photo Library on Mac