Limiting Collabora-Online Editing doesn't work

I have a strange situation with a Nextcloud/CODE installation.

Situation: Nextcloud 20.0.2 with CODE installation via .deb packages on a separate host. Use of CODE is limited to a certain group.

Problem: Users are sending out public links for a .docx document, password protected. When the receiver (not in the above mentioned group) opens the document, it is opened in CODE. Instead the download button should be displayed.

Does anyone have an idea how I can fix this?

Thank you!