To carry out the examples I have used a device with Android 5 and another with Android 9 Xiaomi, in both I get the 800 kB file in 110 seconds at 115200 baud when I transmit from Arduino to the app. From the app to the Arduino it is slower.
We remember that the baud rate that we establish is to communicate the Arduino MCU with the Blutooth module, once the BT module processes the information it is transmitted with a 2.4 GHz carrier.
BTW, other RF transmission possibilities: