My son used to be like that. Then we realised he may not be ready for it yet. So we decided to wait till he can talk.
When he was around 18mths, he can speak in proper sentences and is able to verbalise his needs. So we decided to give toilet training a chance again. My maid will make him sit on the toilet bowl when he wakes up every morning to poop and pee.
At first he refused to poop, only pee. But my maid continued and soon he poop in the toilet bowl. Then we decided to not let him wear diapers at home to train him. Every 15minutes we ask if he wants to pee/poop. Usually he'll say 'no', if he does not answer us, it means yes!
Continue perservering and now he is 29mths old, he goes diaper-free at home. He'll tell us when he wants to pee/poop. Sometimes when we are busy, he'll even go to the toilet himself, pull down his pants/undies and pee, then he'll wear back his undies and pants and wash his hands with soap (oh my, i just typed soup cause I'm watching a show and they are drinking soup!).
If you want your boy to be able to poop without his diapers, you need to perservere Put him on the toilet bowl at the timing that he normally poops everyday.
Btw, my son hates potties. He only wants the real toilet bowl without child seat!