I've been exploring pretty much the same questions for the last few years. The first couple years felt distressing because I didn't feel like I was making progress quickly enough and I had way more questions than answers. Lately, I feel more positive about the direction of travel, and I've made peace with this being a slow, difficult journey. Seems like it should be "easy", but it's really not. Accepting that and not feeling too hard on myself helped a lot.

I haven't figured out a Grand Unified Theory or anything, but a few ideas that seem important to me:

1. Altruism & Relationships - covered extensively here already. Cultivating a few deep relationships and picking altruistic goals seem to be the scalable approaches to escaping the Hedonistic Treadmill and they're probably necessary components of any post-financial independence life strategy.

2. Growth - I'm not sure if this is a universal human thing or just something entrepreneur types are predisposed to, but I've realised that I'm much happier when I'm learning and growing. When the learning curve flattens out, I get feel unsettled. This seems to line up with your observation that you intensely take up a hobby, then shift to something new. Startups scratch this itch well because the company's growth forces constant personal growth. Initially, I tried to transcend this need to always be in motion thinking it was unsustainable over the long term - but lately I've been more accepting of it.

3. Change the Game - the trouble with growth as you approach the peak of whatever career/goal/journey you're on is it becomes exponentially harder to level up and satisfy that need for motion. I think the solution is to pivot to a totally different journey where you can start as a beginner and have a lot of attainable learning & growth ahead of you. I suspect this is a big part of why successful people tend to pursue philanthropy at the height of their careers - it's a whole new game, with new challenges to overcome.

From those ideas, I decided to pick a difficult, new domain to focus on with a goal of figuring out how to do some meaningful good. I happened to choose climate change, but health, education, poverty reduction, democracy, or any number of other issues fit the bill of "hard enough to provide years of learning/growth + focus is helping others". By picking something and committing, I avoided getting stuck in and endless loop of trying to decide what the optimal area is - a bias to action helps a lot when you get stuck with too much choice.

For me, the concrete starting point was Googling "best climate change books", reading half a dozen of them, and trusting my curiosity to guide me from there. I've spent the last year learning, and now I'm converging on starting a startup - although there are plenty of other structures that could work too (non-profits, volunteering, working on open source, consulting, advising, etc). The journey hasn't given me total clarity or magically solved everything - but by imposing some structure ("work full-time to figure out how you can help with climate change") on my life, things are at least less confusing.

Happy to discuss more privately if you'd like.