On Surface Book 3, Windows 10, with the latest drivers and firmware installed (as of today, January 9th 2021), the Nvidia GPU still disappears after sleep (or closing the lid).
One solution that worked for me is to detach and re-attach the display which shows the GPU again the device manager.
Another solution that worked, if you have admin rights, is to scan for hardware changes in the device manager.
However, this is not a permanent fix and I agree with all of you that for a $3k laptop, this issue is
absolutely unacceptable!
I am proposing that we all add our grievance on this topic on the Feedback Hub app. Just type "feedback hub" in the Windows Start Menu and add your complaint. Since I couldn't find a recent complaint about this issue, I created a new complaint.
Search for "Surface Book 3, Windows 10: Nvidia GPU disappears from devices" and you should be able to add your complaint to mine.
If anyone of you already started a thread on Feedback Hub, please let us know, and we'll add our grievance there as well.
Let's see if and what response we'll get from MS.
If anyone of you can think of another, more effective approach, please let us know as well.
Good luck to us all,
Markus