Wow, I can sure relate, as I dropped out of college due to depression when I was 19. I went back at age 32 and finished, but never did anything with what I studied. I had already established myself in a line of work that I stayed in. I had regrets, but my job gave me reasonable economic security. At times, it was very fulfilling. I figured I could always take more courses and gradually move towards a line of work that might seem more fulfilling and in line with my original interests and goals.

Then, when I went to sign up at a University after the age of 50, I was flabbergasted at the level of computer literacy that going back to school would require. I wasn't even computer literate enough to sign up for the d*mn courses. I had to get special hand-holding just to register. I thought, "Good golly, how am I ever going to be able to even write a paper?" I just walked off the campus in despair, probably magnifying the challenge beyond what I needed to. But that's what depressives tend to do.

After that, my job performance just deteriorated.

Good for you getting registered for those classes. Maybe also look into a class in the bio-sciences. You might consider training to work as a peer counselor. I'm sure it doesn't pay anything remotely like would you can make as a plumber, but it might allow you to use some aptitudes that you were born to develop.