How do I add a user to multiple groups?

I need to organize access to the forum so that one user can be in different groups, and that his permissions for each specific forum are determined by the maximum of his capabilities in individual groups.

How can this be organized?

For example, in one section of the forum, a person should be a simple participant, in another-a moderator, and in the third – do not have access at all.

I couldn’t find anything similar in the help and admin panel of the site.