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Azure Spatial Anchors can be implemented on HoloLens 1, but you need to pay attention to the SDK version. Since 2.9.0, Unity 2019.4 LTS is no longer supported due to some known issues. For more information you can refer to Install Azure Spatial Anchors for Unity - Azure Spatial Anchors | Microsoft Learn.
You can also refer to this sample - Quickstart: Create a HoloLens app with Unity - Azure Spatial Anchors | Microsoft Learn, and please pay attention to the SDK version in this sample.
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