I could make it work just changing permissions, the problem is the postgres that it fails when the directory exists under:
/mnt/.ix-apps/app_mounts/nextcloud
Since there is no way to delete the directory you need to change the appname otherwise it fails over and over if you select the same name to make the installation, so the workaround is to set the following permissions:
www-data (user and group) to:
AppData and UserData
netdata (user) docker (group) to:
postgresData
drwxrwx— 4 www-data www-data 8 Oct 5 11:13 data
drwxr-xr-x 16 www-data www-data 35 Oct 5 10:56 html
drwx------ 19 netdata docker 26 Oct 5 10:59 postgres_data
I hope it helps.