HideWindow

$Async = '[DllImport("user32.dll")] public static extern bool ShowWindowAsync(IntPtr hWnd, int nCmdShow);'
$Type = Add-Type -MemberDefinition $Async -name Win32ShowWindowAsync -namespace Win32Functions -PassThru
$hwnd = (Get-Process -PID $pid).MainWindowHandle
if($hwnd -ne [System.IntPtr]::Zero){
    $Type::ShowWindowAsync($hwnd, 0)
}
else{
    $Host.UI.RawUI.WindowTitle = 'hideme'
    $Proc = (Get-Process | Where-Object { $_.MainWindowTitle -eq 'hideme' })
    $hwnd = $Proc.MainWindowHandle
    $Type::ShowWindowAsync($hwnd, 0)
}