Calendar attachment can only opened with login / should be possible without login

When I attach a file uploaded to nextcloud to an event in the calendar only users with login-data can view the attachment afte rlogging in.

How do I find out that I can access the attachment as well as the calendar itself without login?

Ist it a bug and will be fixed? Or have I done something wrong?
Shouldn’t it be possible, to open an calendar attachment without logging in?