I've rekindled by passion by working for a startup again.

My previous employer (which I also joined as a startup) ended up in a situation where the head product manager became VP of engineering (it's a complicated story - don't ask). We also had a yes-man director of Eng and together they went all-in on very orthodox scrum, where they sat in the sprint planning/point meeting and overrode every decision of what to take off the backlog and enforcing "themes" of each sprint to ensure that only product work got done. It was very rare that any tech-debt work got dealt with, and security work was only done if it burned down CVEs or other "quantifiable" metrics that were contractually obligated.

I ended up ok as there was eventually an exit, but the core experienced engineering team all left within 6 months.

Now I'm not only allowed, but encouraged to take initiative and while of course I do product work, I can also take a step back before taking two steps forward again.

Any tips on finding this again? I had a great situation turn sour in exactly this way once growth and leadership change came.

I'd say it's missing the FI part and the RE part of the FIRE strategy. Even if they did retire early with financial independence, it's never been their goal and they never actively worked toward it. The reason regular saving and regular humble living look a lot like FIRE saving and FIRE humble living is that an average person can only do so much to increase their net worth, so the possible variance between any two people is very limited.

"Lived humbly" is vastly different from "reduce expenses and maximize savings" which FIRE is all about. I've basically always earned more than I could spend, although I thought nothing about saving money, does that mean I'm doing FIRE too, or just happened to be "living humbly"?

Figuring out what you want to build isn't necessarily easy.