I had to read your message a few times to make sure I was understanding. If your mower has a hydrostatic drive the only clutch on it is for the blades. That would either be electric or hand operated. Are you talking about the parking brake? But that wouldn't have effect starting the engine. Or are you saying that the blades are spinning all of the time?
Every tractor style mower has a clutch in the drive system.
Remove the battery & deck then sit the mower on its bum.
Under the mower you should see the drive belt that goes through a pair of pulleys on one side.
These pulleys are on a lever with a spring that puts tension on the drive belt.
When you press the COMBINED CLUTCH & BRAKE PEDAL it should pull against the tension spring allowing the belt to slip.
Check the belt run .
check that debris is not stopping the COMBINED CLUTCH & BRAKE PEDAL for retracting fully.