Cannot delete files I created (11.0.0)

I created a folder and shared it with full rights to all users in one group.
All users from group are able to see and edit documents in this folder.

Now if a user creates file in that folder, he cannot delete it, nor I who created the folder and set all the rights. What to do?
Is it possible that admin has rights to edit and delete any folder and file on our nexctcloud? Why this isn’t enabled by default and where can I set it?

Thanks for all your help.

Can you tell us which error is reported and what entries you can find in the logfiles? Could be related to file-locking.