Subsciption to icloud calendar via webcal

I am trying to subscribe to my partner’s icloud calendar, she gave me the public URL to her calendar (“webcal://…”) which I added to my /e/ calendar. The calendar is added without any error notification, but I cannot see any calendar entries. (Using the same URL in google calendar works.)
I did not find any information in the forum, can someone help, is what I am looking for not possible in nextcloud / /e/os?
Many thanks!

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No knowledge of icloud here, but I know that for some CalDAV providers some permissions must be given, including read.
Maybe this could help: iCloud — DAVx⁵