First, open the aio interface and create a backup and start your containers again after the backup is successful.
Afterwards, run via CLI:
Go into the container
sudo docker exec --user www-data -it nextcloud-aio-nextcloud bash
#Now inside the container
Switch to the beta channel
php occ config:system:set updater.release.channel --value=beta
Run the update
php updater/updater.phar --no-interaction --no-backup && php occ app:enable nextcloud-aio --force
Switch back to the stable channel
php occ config:system:set updater.release.channel --value=stable
Exit the container
exit
The above instructions should upgrade you to Nextcloud 29. You might need to follow the steps a second time to reach NC29. If something goes wrong, feel free to restore the backup.
