Yes, I totally can relate to this. I have it, and also have found a recurrence/cycle, sometimes where the interest comes back like 10 years later and goes to a whole new level. Often my hobbies have had to do with processes, capabilities, equipping myself, to the point that it has always seemed with hindsight that the ultimate "goal" of the pattern of obsessions has been this: to take what previously seems almost impossible for a regular person to have or do, and make it utterly commonplace in my life. To make it not a commodity anymore, but that I WANT to take the amazing for granted. And once having achieved at a high level some new ability, I like to put the various trophies on the wall and admire them forever, as laurels. Maybe to indulge in at some future time, or not. Just being able to bask in the reality that, hey I did that.
But I get bad obsessions, fixations, too. Ones that bring me down. I only just realized that. It makes me want to find a way to trigger the Change. Wish I knew how to jumpstart that on purpose. I'm ready for a new and productive hobby. What will it be and when? I hope soon. I've been sad almost 2 yrs now, being "between" good/useful obsessions.