We have an overweight cat any advice on getting him healthier?

OK so we have him on diet food hill prescription diet. The problem is we try to play with him but he won't move around much. If we try the play with one of those toys on a wire(pet safe) he will try to swat it but if it's out of his reach he will just lay on his side trying to reach it without moving. Or he will chase it then give up really quickly.he does have zoomies which is a recent thing. I want to do the right thing by him. We have a cat wheel as well. He will sit in the wheel but won't run or walk on it. We let him outside supervised with a harness but he won't really walk around he will take a few steps and lie down. But yea any advice would be great.