Additional update - service to retrieve the mastodon user ID - https://prouser123.me/mastodon-userid-lookup/
For looking at older classic artists / prog I like the discussions by the music buffs at https://www.youtube.com/c/seaoftranquilityprog mostly for album rankings and then maybe check the best ranked to see if it might be to my taste.
https://talk.maemo.org/showthread.php?t=82997 has the command to use. Where coderusinbox_40gmail_2ecom is the user login and email@example.com is the room.
Pasted below for posterity.
qdbus com.nokia.Messaging / com.nokia.MessagingIf.startConversation /org/freedesktop/Telepathy/Account/gabble/jabber/coderusinbox_40gmail_2ecom0 firstname.lastname@example.org 2 0
Hi Georgy - I can find it via https://email@example.com and am able to subscribe from there -