Does anyone know the name of the film technique where multiple objects fall into the view of the camera which is pointing up and cover up the whole shot?
Specific example is in this clip A Joy Story - Joy and Heron at 3:03 mark.
It's called an Invisible Wipe, or Invisible Cut.
Using an object or person from one scene to cover the entire screen, then as they move from shot another scene is revealed.
Of course, this is easy in an animation, but it's also used in film, even before modern digital editing.
There's a lovely article - Invisible Cuts: a new Trend in Video Editing - which covers many types of transition, including all the varieties of invisible cuts & wipes.
Wikipedia has a title for it (but I don't know if it's actual industry term)
Natural wipe
A transition technique accomplished by an element within the mise-en-scène rather than by a laboratory process. A character or an object is brought to the lens of the camera and wipes away the scene by completely blocking or blurring the frame.
A closing door often serves as a natural wipe. The natural wipe is followed by a new scene. A head-on, tail-away transition is a type of natural wipe that is used to end one scene and to reveal another
The same technique is also used in broadcast, often in sports and transitions into or out of replays. When used this way, it is called a "stinger".
Here we see a graphic fly in, grow and move to fill the entire screen. As the graphic is full-screen, the wipe or transition happens behind the graphic, and the content is visible as the graphic animates out.