Pee pee trained but won't poop on potty - suggestions

DS will be 3 in a couple of weeks. I decided we should potty train (i was in no rush) since he's been waking up dry for months and can hold his pee if he wants to. He also doesn't even poopie when we are out. Waits until we are home.

So, I put him in undies and he's done great, he was peeing in the potty from day 1. Only 1 accident when he was distracted. He's been in undies all day today and has peed on the potty 6 times (drinks lots of water). But, he hasn't poopied on the potty. Same thing happened the other day but later I put him in a diaper bc we were going out and he poopied in the diaper 5 minutes after we got home

I think he has to poo. He said potty 3 times and then took it back. But he touched his tushy. We sat him down with the iPhone hoping he'd relax and poo but after 15 minutes he got up and that was it.

How can I help him poopie on the potty? I bought him some hotwheels (they're in the bathroom) and he knows he will get them when he poopies in the potty. Don't think he cares about them anymore. What should I try?