I have ADHD and when I don’t understand something, feel stupid, or don’t get “enough” done during the day, I totally shut down. Advice?

I have ADHD and when I don’t understand something, feel stupid, or don’t get “enough” done during the day, I totally shut down. I’ve been working on how to work myself out of the “i don’t understand this and am stupid” spiral, but i cannot for the life of me figure out how to be comfortable with the amount of work i get done in a day. No matter how much i get done it doesn’t feel like enough and it leaves me feeling irritable, overwhelmed, and frustrated. Anyone have any brain hacks for this?