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This sample has two branches, from your description, you should use the 'OpenXR' branch, please refer to GitHub - microsoft/MixedReality-QRCode-Sample at OpenXR.
The SpatialGraphNode used in the OpenXR branch is from Microsoft.MixedReality.OpenXR instead of the SpatialGraphNode.cs in the sample. Please check that you are using the correct branch.
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