I really would advise going into a birth debrief with very low expectations, in fact I think I'd advise against one as a tool to heal yourself.
They're often an arse covering exercise. I had one after suffering with similar thoughts to you. Personally I felt I'd failed, If I couldnt birth my baby right how could I be a good mother? I had unrelaiatix expectations of myself (today I won't let my baby cry, I will be perfect, she will be happy, never cry, drink all her milk, sleep soundly for every nap). It all stemmed from the birth.
I had a debrief, instead of making me feel better it showed how shocking my care was. I was repeatedly lied to by the medical staff during my labour so they had an easier time and coerced to make decisions with half truths. The matron who phoned to follow up acknowledged I'd been lied to but told me that it was okay to lie to me as they cared about my baby and needed me to make the right decision.
I can tell you what did help. I had an in depth and private debrief with a doula who specialises in birth rewind services, so focused on my entire labour, delivery and after from my point of view, everything I said was validated and at the end I felt like a new woman.
I'd also add to you, I heard a lot of 'you've got your baby, they're healthy, what more could you want?' It made me feel guilty and selfish. You are allowed to be happy your baby arrived safe and love them completely while also grieving for the birthvyou wanted but didn't get.
I'm happy to discuss further if you want to PM me.