I did what you said and it is working on other games i tested it, but it's not working gor that specific game.
This is what i did
Set WshShell = WScript.CreateObject("WScript.Shell")
obj = WshShell.Run("""Castlevania 3 - Dracula's Curse 2020""", 3, False)
WScript.sleep 3000
WshShell.AppActivate ("Dracula's Curse 2020") 'Focuses game window just in case
WScript.sleep 200
WshShell.SendKeys "%{ENTER}" 'Sends ALT+ENTER to enter in fulscreen mode (720p)