Create account should allow for custom server.
The drop down list should be supplemented with a freetext field for custom server.
The drop down list could use info from the server list here: https://xmpp.net/directory.php and also show the servers security grade in the GUI.
Also under: Add Jabber (XMPP) account -> Advanced Accoutn Settings, theres a "Connect Server" option which can mislead people to think it overwrites the domain chooser dropdown box. But it doesnt .
Either this is a bug , or this field has some alternative function i didnt understand.