@Jack Fields, Thanks for posting in Q&A.
From your description, I know you have configured System Extension policy in Intune but get some error.
To clarify this issue, please check the following.
1.Please check whether your device meet the requirements.
2.Could you please share the screenshot of policy status in Intune portal?
3.Please try to delete the policy and re-create a new policy, then assign it to All Devices to check if the issue can be fixed.
Here is a link about how to troubleshoot macOS configuration policy.
https://www.anoopcnair.com/troubleshoot-macos-configuration-profilesintune/
Non-official, just for reference.
If there is any update, feel free to let me know.
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