@Maximilian Sauer, Thanks for posting in Q&A.
For your issue, here are some steps you can try to fix this issue.
1.Check your network connection. Make sure your device has a stable internet connection or try to change another network.
Here are some requirements for Intune enrollment.
https://learn.microsoft.com/en-us/mem/intune/fundamentals/intune-endpoints?tabs=north-america
2.Try to reinstall the company portal app to check whether the issue can be fixed.
Please try above information, if there is any update, feel free to let me know.
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