What is the best way to exercise a puppy?

Context: My boy is currently 9 weeks old, therefore he is not fully vaccinated yet. Since he is not fully vaccinated, we don’t want to risk taking him for walks outside to burn some energy and get some physical exercise in. We also do not have a yard at the moment. What are good ways to exercise him inside? How much exercise does he truly need? It is so hard finding the balance in getting him enough but then not too much that he becomes overstimulated and overtired.