@Wolf Dominik Thanks for posting in our Q&A.
For this issue, please try the following actions:
1.Please check the "Connection status" and "Last synchronized" time under Tenant administration > Connectors and tokens > Microsoft Defender for Endpoint in Intune portal. It will display if the connection is normal between Intune and Defender.
2.In our official article. it shows that once the connection is established, the services are expected to sync with each other at least once every 24 hours. Please wait and check if it will sync.
https://learn.microsoft.com/en-us/mem/intune/protect/advanced-threat-protection-configure
Hope it will help.
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