Can't create/delete calendar entry in shared calendar via CalDAV

Hi there,

i have the exact same Problem with Outlook and CalDAV on my Windows Computer.
I can’t create and delete but if i create a calendar entry in my nextcloud it gets synced with my Outlook. (so it only works one way)
The Problem is that I am already on version 20.0.4

This is the report for deleting an item:

<?xml version="1.0" encoding="utf-16"?>
<?xml version="1.0" encoding="utf-16"?>
<SynchronizationReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <ProfileName>NextCloud Kalender</ProfileName>
  <ProfileId>xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx</ProfileId>
  <StartTime>2020-12-21T20:56:35.781871Z</StartTime>
  <ADelta>Unchanged: 0 , Added: 0 , Deleted 1 ,  Changed 0</ADelta>
  <BDelta>Unchanged: 1 , Added: 0 , Deleted 0 ,  Changed 0</BDelta>
  <AJobsInfo>Create 1 , Update 0 , Delete 0</AJobsInfo>
  <BJobsInfo>Create 0 , Update 0 , Delete 0</BJobsInfo>
  <LoadErrors />
  <EntitySynchronizationReports />
  <ConsiderExceptionThatLeadToAbortionAsWarning>false</ConsiderExceptionThatLeadToAbortionAsWarning>
  <Duration>00:00:01.0870871</Duration>
</SynchronizationReport>

Second Entry (also for deleting) is:

<?xml version="1.0" encoding="utf-16"?>
<SynchronizationReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <ProfileName>NextCloud Kalender</ProfileName>
  <ProfileId>xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx</ProfileId>
  <StartTime>2020-12-21T20:56:46.9998722Z</StartTime>
  <LoadErrors />
  <EntitySynchronizationReports />
  <ConsiderExceptionThatLeadToAbortionAsWarning>false</ConsiderExceptionThatLeadToAbortionAsWarning>
  <Duration>00:00:00.0329999</Duration>
</SynchronizationReport>

Thanks in advance,
Patrick