This is not meant as a criticism, hopefully more of an inquiry if you so choose. Is it possible that your 'feeling' of your brain being irreparably damaged is actually factually incorrect? And that your assumptions/model of the plasticity of the brain may be wrong and skew a bit negative?
Is it possible that these negative thought patterns are holding you back? Awhile back, I became aware of some irrational negative thought patterns I had myself, and worked on reframing them, and it helped immensely w/ confidence.
This is what therapists have told me, but when my mind totally blanks when asked a question in a meeting, or when I can't vocalize a coherent thought without stumbling over myself, or when I have to read a paragraph 20 times over for the information to stick, I have a hard time believing it's just a negative self-perception.
On examining the negative thought patterns, I think there's at least a couple parts to it:
1. If you very much believe no amount of physical health interventions will have any cognitive effects, then it seems like the probability of you sticking with any sort of health/fitness routine is very low. If in fact, health/diet/fitness DOES have positive cognitive effects (it's been proven scientifically and there are tons of anecdotes), you may end up depriving yourself of a really great thing for improving quality of life and cognition. So examining the possibility that your cognition is not doomed and immune to physical health interventions could greatly increase the odds of improvement.
2. In 2 of your examples, they were social situations. In my experience, negative thought patterns can definitely impact that. I'm saying this somewhat loosely, as I'm not an expert, but have done research in the past on this: Thoughts can trigger bio/physiological responses in the body/brain that can definitely impact cognition.
Is it possible that these negative thought patterns are holding you back? Awhile back, I became aware of some irrational negative thought patterns I had myself, and worked on reframing them, and it helped immensely w/ confidence.
Here's a random link on the general idea (can't vouch for all the content, but it captures the idea of this pattern): https://positivepsychology.com/cbt-cognitive-restructuring-c...