I bought Goguma from App Store and tried the F-Droid nightly repository and while I was able to add one Ergo server which works well with chathistory and all loaded, I cannot find settings for adding other servers anywhere and am thus led to think the feature doesn't exist yet.
Yes, that is correct, it is a missing feature. Goguma supports multiple servers when set up with a bouncer only.
All of the infrastructure is already in place, just need to add the UI to manage the servers.