Recently, a loading screen has been added when reloading resources, such as when changing resource packs, selecting a different language, or triggering a manual reload with F3 + T, in order to avoid the game from becoming unresponsive.

Although, like reloading resources, backupping a world may also be a lengthy operation, and there was no loading screen added to it. Notice when you backup a world that the game freezes momentarily; likewise, a loading screen there would be very adequate, as it would not only prevent the game from freezing, but also show the backup progress in a very intuitive way.