newnormal

That sounds exactly what I was going through for the past 15+ years. I had many strong interests, but everything seemed like more work than it was worth doing. Depression and anxiety accompanied the low motivation. I chalked it up to being in a bad mood, and tried lots of mental health related things to fix that, with little progress over years of consistent effort.

Within the past two or three years, some health concerns started showing up - daily headaches, a near-constant lightheaded feeling, nausea, trouble focusing my eyes, stuff like that. Eventually, the near-constant nausea forced me to try some dietary changes.

It turned out that gluten was the cause of all those more concerning health issues. But to my surprise, it was also the cause of the attention and motivation issues that had plagued me for most of my life. After 3 or so days off of gluten, my mind suddenly felt so much more clear, and since then, I've been much more able to pursue my interests. I didn't get diagnosed, but the closest disorders I could find are gluten-induced brain fog (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7454984/) and the beginnings of gluten ataxia (https://jnnp.bmj.com/content/74/9/1221).

I'm not saying that you have the same thing, but it could definitely be a medical condition if you don't respond well to therapy or antidepressants. I wouldn't overlook the physical side of things.