The directory on https://fediverse.info/explore/people allows everyone to sign up by adding hashtags to their profile, and using the #fedi22 tag to opt-in. Great to use if you are looking for a specific topic.
https://truesciphi.org/ is a curated list dedicated to science, philosophy and mathematics. These are fairly large lists, and great if you want to find scientists in specific fields.
spreadmastodon
maegul