Hi Graham,
Welcome to Microsoft Community.
I'm Hahn and I'm here to help you with your concern.
I'm sorry to hear about the trouble you're having with your Surface Go 3. If only a limited number of keys do not work, it is more likely a hardware rather than a software problem since some keys work fine and you have already tried resetting the system.
The Surface standard limited warranty and Microsoft Complete are applicable only in the country where you purchased your Surface.
If the problem with your Surface is not covered by the warranty or if your warranty has expired, your Surface may be eligible for out-of-warranty service for a fee. Be aware that out-of-warranty service for your device may no longer be available in your region. To learn more, Please contact Microsoft Support. Contact Us - Microsoft Support
Your Sincerely
Hahn. W - MSFT | Microsoft Community Support Specialist