Advice on meeting the needs of a very smart cat

I currently have 3 cats and have had cats all my life- however, my most recent addition is hands down the smartest cat I’ve ever come across. I recognized this pretty quickly and have purchased all sorts of puzzles, which he is mostly bored of. The one activity he does not bore of, and wants to do ALL the time, is playing fetch.

Hes going on 2 years old now and has gotten to the point of dropping the ball directly into my hand if I hold my hand out. If I’m not paying attention to him and the ball is close to me, he will kick the ball so that it hits my foot or is otherwise noticed by me so I’ll throw it. He almost never gets tired of it. I love it and play with him quite a lot, but still feel like it’s not always enough.

I’m always getting new toys to try but nothing seems to come close to manually playing fetch with him. Again, I love it and am happy to oblige, but wonder if there’s more I can do to make sure he’s happy and stimulated.

TIA!