There is a link to unsubscribe below. BTW, I like your idea. AutoCAD has this. You could make a feature request in the bug report page. https://www.qgis.org/en/site/getinvolved/development/bugreporting.html
By the way, can we make polygons shapes with holes or islands??? If so, you can probably use the transparency to simulate what you need.
No, there's no way to achieve this properly using current
functionality. To do it properly we need to ensure that the map
rendering respects the actual shape of the layout map, and doesn't try
to place labels or other symbology effects outside of the actual