How do I get to an isolated folder structure for individual users?

Nextcloud version (eg, 12.0.2):13
Operating system and version (eg, Ubuntu 17.04):Ubuntu 18.04.1
Apache or nginx version (eg, Apache 2.4.25): Apache2
PHP version (eg, 7.1):7

Hello there,
I am facing the issue that every user created seems to have access to all files created by other users. So if user1 creates a new folder, places a file in it, it can be seen & accessed by user2, same vice versa.
I am not referring to default files but new ones created by individual users.
This may be a simple configuration issue but I just don’t seem to be able to figure it out to get every user access to their own files only by default.

Solved - it was all related to an external storage and related permissions…