To upgrade NextCloud, ssh to the VM and do the following:

$ cd /data/www/vhosts.d/nextcloud
$ sudo -u www-data php ./occ maintenance:mode --on
$ mariadb --user nextcloud --database nextcloud -p < /home/installer/backup.sql
Enter password:
$ sudo -u www-data php ./occ maintenance:mode --off
$ mariadb --user nextcloud --database nextcloud -p
Enter password:
> describe oc_appconfig;
> alter table oc_appconfig add lazy tinyint(1) null default 0;
> alter table oc_appconfig add type int(11) not null default 2;
> describe oc_appconfig;
> drop table oc_open_local_editor;
> drop table oc_user_status;
> exit

NOTE! you MUST enable NextCloud's LDAP app before you go any further!

$ sudo -u www-data php ./occ upgrade