Start-TabbyHidden.ps1

function Set-WindowState {

# Source of this function: https://gist.github.com/prasannavl/effd901e2460a651ad2c
	param(
		[Parameter()]
		[ValidateSet('FORCEMINIMIZE', 'HIDE', 'MAXIMIZE', 'MINIMIZE', 'RESTORE',
		'SHOW', 'SHOWDEFAULT', 'SHOWMAXIMIZED', 'SHOWMINIMIZED',
		'SHOWMINNOACTIVE', 'SHOWNA', 'SHOWNOACTIVATE', 'SHOWNORMAL')]
		$State = 'SHOW',
		[Parameter()]
		$MainWindowHandle = (Get-Process -id $pid).MainWindowHandle
	)

	$WindowStates = @{
		'FORCEMINIMIZE' = 11
		'HIDE' = 0
		'MAXIMIZE' = 3
		'MINIMIZE' = 6
		'RESTORE' = 9
		'SHOW' = 5
		'SHOWDEFAULT' = 10
		'SHOWMAXIMIZED' = 3
		'SHOWMINIMIZED' = 2
		'SHOWMINNOACTIVE' = 7
		'SHOWNA' = 8
		'SHOWNOACTIVATE' = 4
		'SHOWNORMAL' = 1
	}

	$Win32ShowWindowAsync = Add-Type -name "Win32ShowWindowAsync" -namespace Win32Functions -passThru -memberDefinition '
	[DllImport("user32.dll")]
	public static extern bool ShowWindowAsync(IntPtr hWnd, int nCmdShow);
	'
	$Win32ShowWindowAsync::ShowWindowAsync($MainWindowHandle, $WindowStates[($State)]) | Out-Null
	Write-Verbose ("Set Window Style on $MainWindowHandle to $State")

}

# Launch Tabby
Start-Process Tabby

# Declare an integer variable to hold the handle of Tabby's main window
[int32]$tabbyMainWindowHandle = 0

# Wait for Tabby to launch, and then hide the window
while ($tabbyMainWindowHandle -eq 0) {

	# Declare an array to hold the handles of all of Tabby's windows
	[array]$handles = (Get-Process Tabby).MainWindowHandle

	# After Tabby is launched, but before its main window opens, the $handles array will only contain zeroes.
	# Once the main window opens, its handle will be the only non-zero value in the array.
	# So, we keep a running sum of the values of the $handles array, and as soon as the sum is non-zero, we'll know
	# that the main window has opened, and that our running sum will be its handle.
	$tabbyMainWindowHandle += ($handles.ToInt32() | Measure-Object -Sum).Sum
	Start-Sleep -Milliseconds 500

}

# Call the Set-WindowState function to hide Tabby's main window
Set-WindowState -State HIDE -MainWindowHandle $tabbyMainWindowHandle