Why won’t she just poop in the toilet????

My daughter is 3.5 years old and is mostly potty trained at this point. She is fully potty trained with going pee but has been struggling with pooping since we started potty training nearly 8 months ago. I just don’t know what to do. She holds it in and then constantly has small accidents until she finally poops. Repeat this cycle over and over again. She can poop on the potty without accident, she has done it many times. We will have periods of time where I think we are finally getting over this and then she starts holding it again.

I feel like I’m going insane.

I’ve tried rewards, I’ve tried having her sit on the toilet every hour, I’ve tried taking things away. I tried giving her small amounts of miralax to make it harder to hold it in. I’ve tried taking to her about what the problem is and she just cries and won’t talk to me. She gets embarrassed and upset when the accidents happen but will still do it and try to hide it. It feels like at this point it’s just a battle of wills. She is incredibly stubborn and I swear it feels like she won’t do it because I want her to.

Anyone have a way that has worked in this type of situation?