Whether it's "poo poo" or "caca". It doesn't matter, just find some consistency among your family for how your are going to refer to pooping.
Maybe it's Dad, maybe it's Daniel Tiger. But, just notice that someone your child looks up to doesn't use diapers.
Help to make it normal that not everything uses a diaper...and that there are acceptable (and unacceptable) places for people & pets to go.
Some kids decide they're done with diapers and just want to use the toilet, but most don't. They need the opportunity to use the toilet, not just a diaper.
There are children who are legitimately afraid of pooping...but don't just decide for your child that's what's happening. Assume they're not scared. Let's start assuming that they can do it!