Welcome no longer exists as a module of its own. Everything it did, and a good deal more, is now Arrival Studio: the message in a channel, an image card, a timed sequence, a DM, automatic roles, a leave message and milestones.
The legacy Welcome page is still reachable, but as soon as your server has Arrival Studio settings it is read-only and every control on it is disabled.
Info
/welcome-test does not exist and never did as a registered command. Testing runs from the Tests tab in Arrival Studio, which sends the real message.