I have a free Jira plan and have 9 active users (while the limit is 10).
My 9th user with active status has access to the board, but can do nothing with the ticket; it is simply inactive for him.
Also, I can't assign him to any tickets. I tried to send multiple invitations, but he doesn't have them (Inbox, Spam, or any folder). I assigned an admin role to him, but he still can only see the board itself with no access to edit it.