When you've bluetooth connected the phone to Uconnect, you're in the Uconnect environment and using its phone and audio features.
on 2020s (and I think 2019s) Android Auto only functions when one has a data USB cable between the phone to the Uconnect.
On my Moto Z3 with usb cable connection, there is sometimes a 5-10 second wait until I see on the 8.4 non-nav screen that the "phone" icon on the low row/home row turns into the "Android Auto" (AA) icon. Sometimes, the phone stays in AA, and I touch the map function on the screen - then the 8.4 screen finally shows the AA icon, and the phone goes back to the normal android screen.
All functions on the 8.4 that aren't through the AA icon/button are pure Uconnect. AA functions are only when you've touched the AA icon to go in the AA environment, but I can seen how one may get confused, as the AA home screen, AA map screen, AA phone screen, various AA compatible apps, etc all look a little different.
The Uconnect low row/home row stays active when you're in an AA environment/screen, and touching any of the other low/home row icons takes one out of AA and back into Uconnect functions.