Well you managed to put together a pretty coherent post at the top of this thread. That involved quite a bit of skill and ability. I know college graduates who can't put together a paragraph. (which is a sad commentary on how colleges hand out diplomas to the under-educated who pay enough tuition money.) You may not be operating at the top of your game. But you are a long ways from having lost all your capacities.

Basically, you need to participate in something where you get some confirmation that you can do something capably. The world is full of opportunities for that. Pick something . . . anything. Start small with a commitment you are unlikely to fail at.