Per the updated systemd.offline-updates manpage: https://www.freedesktop.org/software/systemd/man/systemd.offline-updates.html dnf-system-upgrade.service should have "After=system-update-pre.target" in its [Unit] section since systemd-239. A .service file with this added can be safely used with older versions of systemd too.
Thanks for info. PR https://github.com/rpm-software-management/dnf-plugins-extras/pull/129