Debian input method team:
Currently, unlike with the fcitx packages, there isn't a frontend-all package for fcitx5 which is problematic when I want to use the flatpak port of the fcitx5. Adding the frontend-all package will make the only packages that need to be installed to be im-config and frontend-all instead of installing all frontends manually and tracking each of its own updates. While fcitx-frontend-all is still compatible with this specific use case, I fear it will be deprecated soon.
Chuck