Get involved in local government and get your friends to do the same. State and municipal governments do most of the actual investment in infrastructure, even if the money might in part be federal, and that’s where the decisions get made. Your vote and voice matter, and the players involved eat at the same restaurants you do, go to the same gyms, and live in the same parts of town, for the most part. If you show up to city council meetings you’ll get to know people.

USA has lots of jobs that pay enough to live on that matter. You wont earn 300k as a teacher but you'll earn enough to live, and you'll earn more than if you "do a job that matters" in a poorer country.

Maybe the practical way to do this is to start non-profits, e.g. via YC, and ask for donations from SV.

Some urgent areas include assessing biological and climate tail risks.

You mean “things that actually matter [to me]”?

Or are you suggesting there is only one set of things that universally matter to all humans?