The plates induct, and subduct, converge diverge and slip by each other. But what happens on the boundaries? One goes under one goes over. The boundary stays where it’s at.

If boundaries don’t move. How can Pangea have happened?

It didn’t.
Pac Man Impact Site Hypothesis (-17°, -107°) Pangea didn't happen
Something hit the Earth at -17°, -107°, creating today's topography.
The plates induct, and subduct, converge diverge and slip by each other. But what happens on the boundaries? One goes under one goes over. The boundary stays where it’s at.

If boundaries don’t move. How can Pangea have happened?

It didn’t.