If you use this (!) integration then you should follow this (!) setup, anything people say is not supported (although it may still work, usually this is old setup)
Wrt to Apple, I cannot help as I have no experience here but on a slightly (?!) similar note, the hotmail/outlook integration changed a few months ago and you now need a much more complex connection setup. It may (?) be that this caldav does not work with apple…I checked a few posts and they all seems to show issues with this integration.
Maybe someone else in this Forum knows more?
As I mentioned, there are issues, if you look in the link I sent on the left side: Known Issues, then in GitHub you will find open/closed(old) issues. I am not 100% sure but it does not look good (also based on other reddit posts)
Hey there, I am also very new to HA, so maybe I was only lucky
But I followed the easy button “add integration to my HA” and entered the following in the window that was launched. And everything works smoothly!