You're going to have to learn that, as a laborer at a firm, the quality of work you do is, at best, loosely correlated to your monetary compensation. Sometimes you can do good work, sometimes you can do bad work, but how much you're paid is going to depend greatly on a number of surrounding factors.
So, accepting that there is perhaps not a strong link between doing work that you're proud of at work and being paid well, which would you rather have first?
If you finish work at the well-paid FAANG job feeling like you still have energy to do good work, you can contribute to open source, build some side project, or, even better, none of those things. You can use your extra time an energy learning new things or engaging in a hobby. You don't need to define yourself by your profession.
If, on the other hand, you'd rather not feel like you're just collecting a check from your job, there are certainly positions and fields that will actually ask employees to move mountains. I'd imagine that firms like SpaceX don't have room for desk fillers. There are lots of scrappy upstarts trying to solve big problems, but you will almost certainly make more if you stay parked in FAANG.
I personally am a game developer; the challenges are unique and satisfying and i don't have to worry about whether I'm contributing to something worthwhile. I also make probably less than 50% of what my friends at Amazon and Microsoft are making. C'est la vie.