If anyone is game, Cyanlabs Ford Sync update downloader app makes it super easy to update the maps and sync version.
Thanks themishmosh! I've downloaded the app, and downloaded the updated Sync 3.4 firmware (20136) as well as the updated map (NA119; my car presently has NA118), but I haven't tried to load it onto my ST yet. Don't know that I want to be first.

The program is pretty slick; it not only provides access to the downloads, it will even burn the thumb drive. Looks legit and reliable, but I haven't seen where anyone has used this on a 2020 Explorer, and it's clear the tool was made to work with older vehicles that want to update to 3.4. It definitely appears to wok for cars that already have 3.4 and want to update to the latest version too, but I haven't seen anything yet that shows that a 2020 ST Explorer owner has updated their firmware using this tool. Anxious to hear it works though, as I would love to update both the Sync firmware and the maps!