it seems the following function from the API is using an outdated default value
GeData* SearchPluginMenuResource(const maxon::String &identifier = "IDS_EDITOR_PLUGINS"_s)
An ID with the name "IDS_EDITOR_PLUGINS" is not used anymore since R21. It seems to be IDS_EDITOR_PIPELINE now. Hence, a menu that should appear after the "Extensions" menu now appears in the rightmost position, when using the default.