To the extent the subtle issues I mentioned for non-IM users are still there, one way for a flavoUr to handle it is to not include any IM framework on the ISO.
Not possible for Kubuntu at the moment, as the emoji picker in plasma requires all the /usr/share/ibus/dicts/ in ‘ibus-data’, and ibus-data ‘Recommends’ ibus, so that gets pulled in.
I was pondering setting ‘run_im none’ in the users .xinputrc, as in Groovy the ibus GTK tray icon starts, as starting that is not acceptable. This did not happen in Focal with the ibus/im-config in that release.