To use OMEMO in Groupchat, the Groupchat should be non-anonymous and members-only -- but OMEMO cannot be turned off, Groupchat cannot be used!
Since quite some time I could not use Gajim due to packaging problem. Now when I try it in 1.6.1. version, I see the error message in the group chat, but group chat's OMEMO cannot be even turned off. Basically, this error cannot be remedied, and user is unable to write in the group chat.
If I try to click on padlock icon, I can see message "This is a public group chat, encryption not available".
There is also inconsistency with error messages, where Gajim speaks of "Groupchat" capitalized, one word and "group chat".