Identifying empty vs not-empty folder
It should be visible if folders are empty or if they contain information. Standard templates are used for folder structures, and with cloud based sharepoint it takes a lot of time to look through the folders when it takes 3-5 seconds everytime a button is pushed before the new page is displayed.
Marcelo Sauaf commented
I think it would not work for practical purposes since SPO does not update content we're viewing due to changes made by other users. I mean, if you go to a lib that had empty folders when you got there, and someone else adds content while you're with that lib/folder being displayed, it would not update such "empty" folder indicator you are suggesting. And this could even lead you or other users in a lib view not updated to think it would be safe to delete it even though someone else has added content...
Add item child count to the view.