Read only folders

Hi guys,

here’s my setup:
I have a RasPi 4 running Libreelec/Kodi with the docker addon and nextcloud inside.
After quite a bit of research (all this docker stuff is new for me) I managed to integrate my external drive where my media folders are.

Here’s the actual question now: I want to make sure I have access to my media without being able to mess something up. So I want to make a user who may write only in the Uploads folder and has read only access to the other folders. Seems like a very basic thing but I can’t figure out how to do it with Group Folders (as far as I understand it Group Folders only works with new folders which of course wouldn’t be on the External Drive). Do I need this File Access Controls app?