VBScript SendKeys CTRL+LWIN+TAB?

try this code:

Set WshShell = WScript.CreateObject("WScript.Shell")
WshShell.SendKeys "+(^{LWIN}{TAB})"

Just in case someone land here on these years...
A workaround (instead of sending keystrokes) is to call directly to the application:

Set objShell = CreateObject("Shell.Application")
objShell.WindowSwitcher

This will open Task Switcher Windows App. (Same as ⊞ windows+TAB)