You get to keep only enough to maintain a very modest lifestyle in a low-cost-of-living area, the rest of it has to go towards improving the world in some way.
Edit: Given the previous rules that you must maintain a very modest lifestyle in a low-cost-of-living area, would you rather choose to opt out and not have the money at all?
Best that I can think of would be to create an endowed institute of political scientists, psychologists, neuroscientists, linguists, et cetera, dedicated to studying and developing ways to counter right-wing populism, and de-program people who fall under its sway.