I think you should be able to tell people that you already know these things as soon as they started their explanations.

Perhaps in your attempts to be agreeable and polite you come across as you really don’t know these things so they keep on going on with their explanation.

Is it possible they assume you don’t know things because you don’t tell people you do? If somebody starts showing me things at work that I already know how to do, Id stop them and said “I know how to do this and now I am busy. Bye.” Well maybe not that rude lol but you got the point, I am not wasting my time listening to things I know

I think some dose of assertiveness is due. Are you seeing a therapist? Some type of role playing would be good. Like how to respond in those situations