With a re-locked bootloader there is no way to upgrade from 6.x to 7.x without doing a userdata reset as noted in the “News” app post on your device and this discussion: Fairphone 4 update to iodéOS 7.4 as well as our issue tracker: Fairphone 4: v7.x builds blocked due to v6.x locked bootloader upgrade issue (#71) · Issues · ota / issue-tracker · GitLab