Discussion spaces, the members in them, and what they post.
A space is a room
Every discussion happens inside a space. Spaces are separate from each other and can be enabled or disabled one at a time.
Whether a member starts pending is a setting
Community settings carry a membership mode. Under approval required or invite only a new membership is recorded as pending, and until someone makes it active that person is not a full member. Under open — the default — they are active straight away and there is nothing to approve.
So before treating a pending queue as broken, check the mode: an empty queue on an open community is correct, not a fault.
A member can also be banned, which keeps their record and only removes their ability to take part. Banning is not deleting — and that is right, because the discussion history stays.
Spaces can require a membership tier
A space can be restricted to a tier of membership. Someone without the required tier does not see it.
So "a user says they cannot see the community" usually has one of two answers: their membership is not active yet, or their tier does not reach that space.
Taking part is never anonymous
Every post and comment belongs to a member.
A member is not always a customer, though. There are two ways in: signing in with an existing customer account, or a one-time link sent to an email address. Someone who joined by link has no customer account behind them — which is why they cannot receive in-app notifications, and why their approval is sent by email instead.