Is there anyway you can disable selection of actors in the scene? I would like to do visualisation of a grid there by placing an actor, but the grid overlay prevents me selecting on actor underneath it.
As far as I know this functionality is still missing in the editor. What you can do for now is to Lock Actor Movement so that noone will move it inside editor (in the World Outliner right click on the object → Transform → Lock Actor Movement). You can use it together with hiding objects on the scene (eye icons in the World Outliner).
It’s not exactly what you wanted but maybe it will help a bit.
Check how epic do this in Landscape Editor mode
bool FEdModeLandscape::IsSelectionAllowed(AActor* InActor, bool bInSelection) const