Howto limit access to user's own user-made content?

I found this script from Raffaelj’s very useful site.
https://github.com/raffaelj/cockpit-scripts/blob/master/permissions/restrict-content-to-owner-and-disallow-editing-published-entries.php

It seems that this is the right way to isolate data.
I also found something about separation of private assets
https://discourse.getcockpit.com/t/private-assets-per-user/1560/3

This is basically what I’m looking for.

Are there maybe more complete scripts or addons that can solve this,
or do I have to fix scripts in various places to achieve this.

Sorry for the stupid questions, but I’m trying to learn cockpit from scratch.

When I use the backend to store permissions for colletions, they all are red,
and when I configure them to green, after saving they’re back to red again.
So I’m very unsure how and if the permissions shall be handled correctly.
Do I have to set all CRUD permissions in the group definiton file, I use YAML ?

Maybe someone could point me to the latest solution for such use case.
Do I look into the right direction ?