Yeah +1 for divide up your tasks
I don't have ADHD but I can still sit in front of an open project and just stare into the abyss of all the different options and ideas and possibilities.
One thing that really helps me when this is happening, is to just WALK AWAY for a little bit. Going outside and just spending a few minutes enjoying nature, or doing some task that doesn't require a lot of critical thinking like washing the dishes, can be so helpful. Often while I'm doing that I ask myself "OK, what exactly should I be working on?" and try to come up with something concrete. Then I can sit down with already the thought in my head "I'm going to do XYZ", so I can just get right into it instead of spacing out or just endlessly "testing" my game while thinking of ideas.
Sometimes I find it helps to pick something really small and seemingly insignificant. For example, lets say I expect to work on a game for the next 2 hours. That's not a small amount of time and so right at the beginning of that time slot is when I might start wondering, what am I going to accomplish in the next 2 hours? This can become one of those times where I'm just spacing out, with too many options.
Instead, I'll decide to just start with one small task. Like, make a single sprite. It is not something that will take up two hours. But it at least gets the ball rolling, and often by the time I'm finishing that task, I have a better idea of what I want to do next. And if not, then at least I got one sprite done :P
With CFS, it is probably even more important to just work in small amounts and take a lot of breaks. Also, all people benefit from sunshine, fresh air, exercise, and good food, so get as much of that stuff as you can!