I am also a 46-year-old doctoral student and have ADHD. I wonder if there are resources you have come upon that assist you in doing work that requires you to do things that aren’t hard, but aren’t interesting.
I don’t mind difficulty. In fact, I am getting an A in grad-level stats. But I am finding 6-page papers on not-very demanding topics really tough.
I get stuck in the “what the heck will I even say?” phase for way too long. Give me something I am passionate about and I will write a stellar paper, but something mechanical and not philosophical and I am lost.