When the resolution is locked for example 800x600, it is most likely due to a graphics card problem.
This can have several reasons:
Graphics card is not activated
In some cases, the graphics card may not be activated at all. To fix this, open the Device Manager panel. Under the Graphics Cards tab, right-click on the Graphics cards and select Enable.
Graphics drivers are not installed
If this is your first connection on your Shadow or after connection a reboot, the graphics drivers are not yet installed. You can download them on the Nvidia website directly or check the instructions here.
Graphics drivers are installed
If the latest graphics drivers are installed, Shadow has been rebooted and the resolution is still blocked in 800x600, you can create a custom resolution using this guide How to set a custom resolution