macOS tries to create default calendar (invalid CalDAV spec?)

[KarlKeu00]

Hello,
I am currently writing a CalDAV implementation with this library (v4.4.0) with customized and already existing backend (HumHub). So far this library works very well, however I am having a couple of issues with macOS (13.4).
Aside from the contacts app only being able to display an address book, there are much bigger issues with the built-in calendar app. Currently, the Calendar app tries to create a calendar when I set up the account, even though I don't prompt the app anywhere to do so. Is this due to the library, or am I missing something?

My code: https://github.com/KeudellCoding/HumHub-Modules-HumDAV

I have intercepted the packets. The following happens when the calendar is activated:
(X-Sabre-Version response is on 3.2.2, although I use version 4.4.0)

1. PROPFIND without Authorization Header to principal URL --> 401
2. PROPFIND with Authorization Header to principal URL --> 207 Principal infos
3. OPTIONS without Authorization Header to principal URL --> 401
4. OPTIONS with Authorization Header to principal URL --> 200
5. REPORT without Authorization Header to principal root URL --> 401
6. REPORT with Authorization Header to principal root URL --> 200 Principal column names?
7. REPORT without Authorization Header to principal URL --> 401
8. REPORT with Authorization Header to principal URL --> 207
9. PROPFIND without Authorization Header to calendar home URL --> 401
10. PROPFIND with Authorization Header to calendar home URL --> 207 correct list of calendars
11. MKCALENDAR without Authorization Header to calendar home URL with some GUID --> 401
12. MKCALENDAR with Authorization Header to calendar home URL with some GUID --> 403 User did not have the required privileges ({DAV:}bind)

I have only read access enabled everywhere because I haven't implemented the write features yet, but it should still work, right?

Thunderbird works perfectly and integrates all calendars without any problems.

Maybe someone has an idea.
Thanks
KarlKeu00