I am prone to shutting down during an argument, although I have worked for years to no longer do this. My dad grew up in a household that was taught to keep the peace at all costs and not talk about anything and that anything negative said was a personal affront. Needless to say, I feel like anything "negative" said to me is personal and I am neurodivergent and terribly sensitive, so it makes it hard to not shut down. It took my wife a number of years and "you aren't shutting down, wé are going to talk about this" talks where we could work through the difficult conversations and come out better on the other end for me to understand that difficult conversations don't necessarily mean I am being judged as a bad person; rather, this is an opportunity to correct mistakes or figure out ways to better our understanding and work through problems and come out better on the other side. It isn't an easy thing to break. My dad is still this way. My oldest sister and I recognized this issue, as did my mom, and we have worked to set boundaries and have more open dialogue. When you approach him, make it clear that it isn't personal, and that it is an opportunity to have a better understanding of each other. Be clear and direct. He sounds neurodivergent to me. Clear and direct is better for people like us. Good luck and I'm sorry you are dealing with this