Which method would make sense to create subgroups in Openfire? Openfire has such a plugin etc. is there? Can I solve it without creating a custom table?
I want to create subgroups linked to a group. They must be able to use all the features of the group they are affiliated with, such as member privileges, etc. Is there a good solution to this?
You're likely referring to multi-user chat groups (as opposed to user-groups).
Openfire does not have support for the feature that you're describing. Using the development API of Openfire, it might be possible to create a plugin that adds these features.
Another approach that you could consider is to provision chat rooms using some kind of external orchestration process. For this, you could use an XMPP client connection with a user that manages the rooms, or the Openfire REST API plugin.