How can I show only Cases that have no Case Manager?
If you set up the page view as mentioned in your other post here, you can add a global text field with a rewrite to civicrm/contact/view/case?id=[id]&amp;cid=[id_1]&amp;action=view.

If you need to set it up for folks that may have multiple case types then filter this page by a single case type.

After you have this view behaving as desired, add an attachment and on the attachment, change the case type filter to your next case type.

Add an attachment for each additional case type.