Thank you for contacting Intel Support,
As I could understand, it seems like you are having problems with your unit as the screen seems to be flickering. I apologize for any inconvenience this may be causing.
Regarding this problem, there are several steps we can try to follow:
1) Please try a different cable when connecting the unit.
2) Please try a different interface for example the mini display port or HDMI.
3) Please try a different monitor to check if it is a monitor or Nuc issue.
4) If the graphics driver is not updated, please try updating it to the version 4849:
I hope you find this helpful.