I wrote an essay about this topic a couple months ago that you might find applicable
https://www.amplenote.com/blog/what_makes_long_term_personal...The essay describes exactly half of the what has helped me, which is to create processes that make it a little bit easier to procrastinate on long-term goals and then pick them up again later. But the other half, which sounds especially applicable to your situation, is to pick a goal that will continue to be worth pursuing. This is much harder than most people expect.
A few years ago I started a "goal of the month" list with some friends. In January, we picked 12 goals we'd pursue during the year. For the first few months, it was gravy -- everyone completed their goal and had a satisfying summary ("I did this, I learned this") they shared with the group afterwards. But, around the 6th month, the failures began. Between the 9-12th months, our cumulative success rate was lower than 50%. It was mystifying, because everyone had purported to spend hours of time carefully choosing their 12 goals in January.
In my case, I tried to pick easy goals for month 9-12. For November, I picked the goal "bowl a 200" because what could be more fun or easy than going bowling (though I've never bowled above 150, so there was a hill to climb). Still, by the time 11 months passed, there had developed 100 things that were more interesting to me than bowling a 200. I willed myself to go bowling one time that month, and scored 125. ¯\_(ツ)_/¯
We tweaked the rules for the list the following year so you set 12 months worth of goals, but you could substitute a goal if your original choice was no longer interesting. Again, by the 9th month, everybody was substituting like crazy. The goals list experience taught me that my friends and I are woefully bad at choosing goals that will still be interesting to us 6+ months in the future.
Fast forward to today, and I've been working on Linux touchpad drivers for about two years now (e.g., https://bill.harding.blog/2019/03/25/linux-touchpad-like-a-m...). My "success" on this project has been made possible because I have a good system to allow myself to procrastinate, and because every time I use my Linux laptop, I continue to hate how the touchpad works. I am forced to face that unpleasantness over and over again, with no escape. So in this case, there is a goal that has remained important to me because it involves a part of my life that remains constant, and remains frustrating.
Which is to say, if you can find a problem that is going to continue to eat away at you for years, I think you're barking up the right tree. If your goal is one of whimsy or interest, your best bet is to scope your solution so it can be completed in 6 months or less, because chances are your human interest will be somewhere else past that point.