Why you can't select a viewport on a sheet

There are many one to achieve something in Revit; Alternatively, there are many ways to troubleshoot something going wrong in Revit. This Revit Recess entry will show 5 ways in which we can make a viewport not selectable. There are obvious pro's and con's for this method.

In the examples below, one viewport has been placed on a sheet.

Example 1: The viewport has been selected and Hidden in View > By Element.

Solution 1: Unhide the viewport.

Example 2: The viewport is pinned and the Select Pinned Elements selection option has been unchecked.
Solution 2: Enable the Select Pinned Elements selection option, and unpin the viewport

Example 3: The viewport has been activated
Solution 3: Deactivate the viewport

Example 4: All Annotation Categories have been turned off in the sheet's Visibility Graphics
Solution 4: Make all Annotation Categories visibile

Example 5: The viewport is part of a Selection Set Filter and the filter is turned off in the Visibility Graphics
Solution 5: Turn the Selection Set filter on