[@bbbt Participant 2 hours, 40 minutes ago]

Thank you for your prompt response.
The hook bbp_new_forum_post_extras is not being called.

I have now tried the hook bbp_insert_forum. It is being called. To ensure that it is a group forum, I then ran the following query:
$group_ids = get_post_meta( $forum_id, ‘_bbp_group_ids’, false );

$group_ids does not yet exist at this point. I only want to call add_post_meta( $forum_id, ‘_private_group’, ‘group1’, false ); if it is a group forum.

Best regards