@Adrian Teuscher , Thanks for posting in our Q&A.
Based on my research, there's no such policy in Intune to disable Google assistant. Then I go to check under Android MDM. I find there's no such feature under Android MDM as well. In fact, Intune use the APIs which Android provides to develop the feature. If the feature is not provided by Android MDM. We can't have this. You can feedback to Android to see if we can get this feature in the future:
https://developers.google.com/android/work/requirements
Note: Non-Microsoft link, just for the reference.
Thanks for your understanding.
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