jabber.org is currently pre-filled into the server field. But I'm not sure jabber.org is still maintained: https://xmpp.net/result.php?domain=jabber.org&type=client
Summary: Show a better server default on account creation than jabber.org → Update default domain in the JS-XMPP account wizard
It seems to be back up now. Still we should check in-band signups work on that server once that bug is done.
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