Ford dealership included the air deflector after all. The ST was in the shop for a replacement speed sensor and they were very kind to include the air deflector part in the warranty. It is an OEM part for the 2020 ford explorer ST. But the service manager mentioned it could not be found when searched as an included part. The OEM part
link sent to the dealership shows it does go on the 2020 Ford Explorer ST. No idea why it shows up in the database as not included.
It looks way better than it did without one on! The big gap between the mufflers always looked off to me. I love it!!!!