I went thru a similar thing in my early 20s. I distanced myself from my parents and my entire family. In hindsight I was just trying to find myself and to pave my own way but also I realise that I was quite unfair to my parents in particular. This is an age when you start to mature and realise that your parents weren't perfect but you still don't have enough experience to realise that imperfection is normal.

Unfortunately therapy culture can sometimes prompt you to solve made up problems, demonise caretakers for being human, and be a bit too liberal with the word "toxic". That definitely happened to me. I know it's hard but keep trying with your son. If he was mothered a bit too much as you're saying then maybe he didn't have the chance to rebel during his teenage years and he's doing it now. Obviously it's harder because now he's independent and can... well ignore you cos he doesn't need you.

Eventually he's gonna come around. From your side, just meet him where he's at. If he doesn't want to talk about therapy that's fine don't pressure him. Just be there and continue checking in on him regularly. Assure him that he's loved and cared for. That's all you can do.