You're not completely accurate on this. I've had my truck since July 2020. Yes, there are 2 navigations for these trucks. Both work with Onstar. All lower trim trucks came with a navigation system that didn't use an on screen map. You could contact Onstar and have them send the turn by turn instructions to your truck, but there's no map. This navigation has been changed to Chevrolet Maps+. This update provides a typographical map. You can ask it to give you driving instructions, but I have found it doesn't trinkets a lot of addresses.
The 2nd navigation system utilizes the SD card reader in the center console, uses a map on the screen, and was only available on LTZ and High Country trucks. OnStar will also send turn by turn instructions to this navigation system, and you'll see it on the map, too. This navigation system where live traffic, etc are displayed on the map via Onstar is this one.
Both navigation systems provide the same turn by turn instructions on the DIC, too.
I think I'm in a rather unique situation here where I have both (Maps+ and SD card) navigation systems in my truck. I added the SD card based navigation system to my truck via MVI. I prefer the SD card nav over both the old turn by turn instructions and the newer Chevrolet Maps+. I have the top Onstar subscription and get the full benefits of traffic, school zone reminders, and so much more. The only thing Chevrolet Maps+ gives me over the SD card nav is the speed limit of the road I'm on. I have noticed Chevrolet Maps+ isn't always accurate on this, and the solution for this is the same as the SD card nav -- eyes on the road and paying attention to signage and speed, duh. The SD card nav also allows split screen view on the radio so I can see the map/turn instructions and the radio/phone controls. Chevrolet Maps+ doesn't allow split screen.
Sorry for the rambling long post. Just wanted to be thorough.