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HoloLens doesn’t support establishing a TCP/IP connection over USB, and IPOverUSB is only used by VS debugging or Device Portal. All classes of USB-C devices HoloLens2 supports have been listed in this link: https://learn.microsoft.com/en-us/hololens/hololens-connect-devices#hololens-2-connect-usb-c-devices.
Currently, you are recommended to communicate with Arduino over the network. Besides, you can provide more information about your request and submit a feature request via feedback hub on new feature request to be considered in future releases of HoloLens OS and devices. If it's a hot impacted feature, it will be possible to be given priority to jump in the development schedule.
For how to post feedback request, you can follow this doc: Send feedback to Microsoft with the Feedback Hub app.
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