To upgrade and disable maintenance mode manually:
runagent -m nextcloud1 occ upgrade
runagent -m nextcloud1 occ maintenance:mode --off
It’s the same Nextcloud version (30.0.10) as 1.4.3.
If nothing helps you could try to change the version in config.php, see also Failed update on NS7.9 to NS8 migrated NextCloud - #21 by mrmarkuz