When I use the term robust for the feature I have in mind I do so because there are some options in place for controlling access to files. However they seem limited and sometimes needs to be done in less than ideal ways.
Essentially I would expect this to be a top priority in any sort of cloud/file sharing system and maybe there is already something in the works I am not aware of, apologies if so.
I envision an admin menu or a view for each folder/file where you can select a user name, user group, etc. and then specify what permission(s) they have, read, create, change, delete, etc.
Without something fairly straightforward like this built into the core I find it hard to believe Nextcloud would ever be used by major corporations.
I will likely add more details to this if there is a conversation here but so far my research has not found anything capable of limited access to folders based on roles at my workplace. e.g. admin can access everything and then a user group can access some things but not all.