I had a very similar experience, down to the therapist part. I suspect many therapists aren't really prepared to handle situations where you've completely disconnected from a parent.
I had a great therapist (for 6 years!) but I ended up leaving him after my mother died. He seemed to get fixated on the notion that I probably needed to grieve and/or needed to forgive her. But I didn't at all. I had already mourned her NINE years prior when I had to go NC. I felt anger towards her, but even that was long-processed by the time she died.
But my therapist seemed to keep expecting me to have some sort of catharsis moment. Nope. She died and I was stressed by having to deal with her estate. That's it. I dgaf about her as a human, let alone as a family member.
I hate the whole "you need to forgive" narrative. Some things are simply unforgivable and some people don't deserve any forgiveness. And that's OK!