These are the following Hitman speedrunning discord servers:

Hitman Runs Server (the "official" Hitman speedrun.com server)

• Best place to ask a general question regarding speedrun strats or run rules, and get information about announcements and polls for Hitman 3 speedrun.com leaderboards

Zebulaus (Server run by Zebulaus, a knowledgeable community member.)

• Good for more specific questions about a certain main mission speedrun strategy.

Frote's Server (server ran by Fortheseven aka Frote)

• Generally good Hitman knowledge, but not really focused on speedrunning main missions)

Well, Zebulaus and Frote's are both not officially affiliated with speedrun.com.

The "official" Hitman Runs server is the best place to get information on future announcements or polls regarding the Hitman 3 speedrun leaderboards, even if people don't chat here all that much.