Sorry to hear about your Google Nest Hub, but thanks for bringing this up.
I know how challenging it can be not to have a working device when needed. A few questions - when and where did you purchase your device? Do you see a hole or service port at the back or bottom of your device? Also, it would help us a lot if you could send a video showing the issue, so we can check further what's going on with your device.
Looking forward to your response.
I agree with you. That is a demo device, and Google will not be able to replace it because it's not intended for sale. I suggest that you communicate with the store where you bought it from and ask for a replacement from them.
Let us know if you need further help, and the community will be happy to assist you.