Talk to Pediatrician on Potty Training

My child is 4 years old. Alhamdulilah active and healthy to school and achieving all the milestones on time. He is fully pee trained. But the problem arises when he has to poop. Most of the day he is diaper free and rush to the washroom to do pee but it comes to poop he asks for a diaper. I tried all the things potty seat rewards and everything but he can't poop in commod. I am really worried. What could be done plz guide