InArcMap, there's a floatingOverview Mapthat shows you the area surrounding yourData View with an extent rectangle showing where you arezoomed. InArcGIS Pro, we need the same thing, an Overview Map to view the extent ofzoomfor the Layerstab.
In ArcGIS Pro you can create a linked map view, but you can't add an extent rectangle unless you have a layout. A layout is not needed here. We just need a floating overview map with an extent indicator.
This problem would be improved by enabling any linked map to have an extent rectangle for the map it's linked to. That would not be as easy as it is in ArcMap, but it might be sufficient. To have full ArcMap equivalence, you should have a button/menu-item for the Overview Map that would just pop it up with the extent indicator present.