I strongly second this- its a well-studied and well-resourced organization that has spent most of a decade investigating the precise kind of question you're asking (namely, how one can best position oneself in life to have a positive impact on the world.)

In particular, they're very clear that there are a large number of possible areas to aim at that all offer the chance to make a big difference, and that there are a wide range of skillsets that can be applied in various ways (you don't have to go back to school and become an engineer.)

I second this site - it's research-based and takes an objective view at several factors including how solvable a problem is, how many people are already working on it, etc. The podcast they host has some great interviews as well.

Marta - I find myself on a similar path and I wish you the best of luck going forward!