[Forum spam prevention] Set to apply to become a member of BuddyPress

The convenient point of including BuddyPress is in the “membership application” section. If you only use bbPress, new members cannot join unless you allow user registration, but if you set up the BuddyPress member participation requests, you can accept requests to join the forum even if you turn off “Allow anyone to register” on the WordPress side. You will have to manually approve members, but this will help prevent most spam registrations.