Hi Marc,
Welcome to our community! 
I don’t know to what you are referring. Maybe the gizmos are disabled in the Scene window? There is a “Gizmos” button in the top horizontal menu of the Scene window. If it is not visible, make the Scene window larger. Click the “Gizmos” button to see if the guidelines appear. If they don’t, click the arrow button next to “Gizmos” and check if the icons/gizmos for the chinemachine are disabled.
See also:
- Forum User Guides : How to mark a topic as solved