Earning to give (to the top charities) is likely orders of magnitude more effective than most other volunteering options.

Research effective altruism and see GiveWell’s most effective charities list (updated a week ago).

Recommended listening: Sam Harris interviews the founder of effective altruism. https://samharris.org/podcasts/being-good-and-doing-good/

Recommended reading: Doing Good Better by Will Macaskill.