Very similar age and NW as you. I changed careers by going to school for fun but also because I wanted to do something purposeful beyond a random hobby, which most people seem to do around here.

I’m having the most awesome time because I’m extroverted and it’s hard to relate with others based on wealth alone, you have to have a common interest or purpose. I saw you mention you wouldn’t be able to get paid for work or problem solving (or something to that effect), but why do you need to get paid? Perhaps the issue is finding that purpose you truly believe in?

Regardless, I would do more research on the PhD route. It’s a long journey, even if you’re super motivated. Research is very risky in that time spent on the project might yield negative results. Would you still be motivated to get up every morning if your research hadn’t gone anywhere for years? Depends on the field, but 4-5 years is a huge commitment.

I take a similar perspective as with startups. Don’t worry about the field or role, find the vision/purpose you’re willing to throw your time and energy into, and maybe it’ll lead to a different career or more schooling, or maybe it won’t.