Most children are potty trained by age 3 but sometimes children are not ready fully to potty train until as late as age 4.
I wouldn't worry too much or put too much pressure on your child about potty training until they're 4 years of age and still showing no interest.
If you do want your child potty trained at 3 then you're gonna have to stop putting the child in diapers and put them in underwear and deal with the messes.
A child will have wet and dirty underwear and make messes during potty training but eventually the child will decide it's much better to use the toilet instead of having wet or dirty underwear and clothes.
Make it a game and reward the child when they go poop or pee in the potty instead of having accidents.
However never punish the child for accidents when they don't make it to the toilet but instead clean the mess up and tell them it's okay and that they can try again later.
Whatever you do don't give in and put the child back in diapers after beginning potty training since that will cause the problem to start all over again.
Once you remove the diapers don't let them wear the diapers anymore and put them out of view of them if you have other children who're in diapers or get rid of the diapers altogether so the child doesn't have a chance to see them and want them again.