Having gained familiarity with the basic functionality of RealityComposer, challenge yourself to create a simple AR scene with behaviors using prebuilt models or some imported from Sketchfab. Some possible scenarios with the basic models:
A pool table/bowling lane where the ball flies into the other balls when tapped
"kicking" a football through the uprights
A rocket ship flies into space with sounds (and then slowly comes back to its landing spot)
Whatever else you want!