Useful Script for Surface Book 2 to toggle off GTX when attempting to detach the screen.

ToggleGTX.ps1

# Useful script for detaching the screen of Surface Book.
# Run if detach light blinks red indicating that it cannot be detached
# since applications are preventing the detach.
#
# Option 1: Copy-paste into powershell window.
#
# Option 2: Run as PowerShell script (requires execution policy change):
# https://superuser.com/questions/106360/how-to-enable-execution-of-powershell-scripts
#
Try {
	$GtxId = (Get-PnpDevice -FriendlyName "*GTX*").InstanceId
	echo "  DeviceID = $GtxId"

	echo "Disabling GTX."
	Disable-PnpDevice -Confirm:$false -InstanceId $GtxId
	Read-Host -Prompt "Safe to detach. Hit enter to re-enable." 

	echo "Enabling GTX."
	Enable-PnpDevice -Confirm:$false -InstanceId $GtxId
} Catch {
	$ErrorMessage = $_.Exception.Message
	$FailedItem = $_.Exception.ItemName
	echo "Try Run as Admin."
	echo "ERROR: $ErrorMessage"
	echo "ERROR: $FailedItem" 
} Finally {
	Read-Host -Prompt "Press any key to quit" 
}

Super handy script, thanks!!

Adapted it a bit, so that it automatically asks for admin permissions if necessary and also automatically toggles between enabling and disabling the GPU based on the device state, so the command doesn't need to be interactive, and you don't need to keep the PowerShell window open while in clipboard mode:

if (-NOT ([Security.Principal.WindowsPrincipal][Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole] "Administrator"))  
{  
  $arguments = "& '" +$myinvocation.mycommand.definition + "'"
  Start-Process powershell -Verb runAs -ArgumentList $arguments
  Break
}

Try {
	$Gtx = Get-PnpDevice -FriendlyName "*GTX*"

  if ($Gtx.Status -eq "OK") {
	  echo "Disabling GTX."
	  Disable-PnpDevice -Confirm:$false -InstanceId $Gtx.InstanceId
  } else {
  	echo "Reenabling GTX."
	  Enable-PnpDevice -Confirm:$false -InstanceId $Gtx.InstanceId
  }
} Catch {
	$ErrorMessage = $_.Exception.Message
	$FailedItem = $_.Exception.ItemName
	echo "ERROR: $ErrorMessage"
	echo "ERROR: $FailedItem" 
}

Thanks! @GleasonK @jonaskuske