From another similar post https://learn.microsoft.com/en-us/answers/questions/277263/dongle-replacement.html:
The Microsoft keyboard and USB dongle are paired and will only work with each other, so the dongles are unique and come as a set.
The frequency between the receiver and device are matched. USB dongle is coded to work with just your device , so a replacement is not possible to get.
Please try contacting Microsoft Store Support:
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