I know some folks (who I consider intelligent) who can't deal with multiple things demanding and competing for their attention.

I wonder if you might do better at a job where the tasks are few, the focus is deep, and you generally don't need to collaborate with or manage other people, rather than a job that requires you to spread your attention broadly and interact with many other folks.

'Few tasks; deep focus; solo work' tends to have a large overlap with artistic endeavors, such as woodcarving or painting, where you can focus on your craft with few to no distractions. If you are artistically inclined, it might be worth consideration.

Edit: Another factor to consider is what appears to be social anxiety. You mentioned shutting down in social settings. It might be worth exploring the root causes with a psychiatrist?