Several thoughts, somewhat unsorted:
- There could be an underlying medical problem. Mild depression often has low willpower as the most noticeable effect. If it's not too much of a hassle, maybe get your thyroid checked. And whatever works for depression should usually work for your problem as well, exercise unfortunately being the most effective
- If what you're doing really doesn't interest you, it doesn't make much sense to see a pathology where everything is working as intended. Try something new (as a hobby maybe) that requires similar levels of engagement, and see if the problem persists. If not, it's time for tough decisions.
- There's a theory that willpower works much like a muscle. There's a book about that phenomenon, but it really doesn't have much more content than the last sentence. It's one of those results that I don't completely trust, but trying it out doesn't cost much: do anything that requires willpower regularly, and see if you improve. The examples from the book were really small interventions, such as brushing your teeth with the non-dominant hand. After three weeks or so, people were significantly more likely to successfully stop smoking, compared to the control group. That's a rather big effect.
- Try reducing your work hours. Being "always on" just drains your resources. Start with restricting your daily work hours to something like 3h or even less, and only expand again if you're productive in those hours.
- Somehow get your hands on ADHD meds (or, you know, the generic alternatives that fuel the bitcoin boom). You'll be as focussed as you ever wanted to be, and even a one-time experience can be helpful, by reminding you what it actually feels like to be "in the zone".