It has been a while since I made it, but nothing much has changed in the AppInventor support for BLE as far as I know, except this permission stuff. The version of the micro:bit does not matter. You can even connect to a V1 micro:bit, although it will run out of memory much faster.
What I saw in you .aia is that you actually never connect to the micro:bit, so no wonder.
Try my tutorial here: App Inventor, Micro:bit and UART
It does exactly what you need, except that you may need to add permissions.
Something else to note: in makecode, go to settings->project settings and set: No Pairing Required.
That will save you a lot of headache.
Concerning the .hex app, I am not so sure it will work properly. You have to be very careful, or else it will run out of memory. Look at mine. It works.
I made some apps to control a robot car, but as said it is rather limited, momory is never enough.
Also it is a real pity that the BLE extensions were never properly updated, but if you use the really old one for the microbit (UART only) it will work.
Let us know how you go.