Thanks for the update Paul. We’ve been successfully using external BT modules. First the SparkFun BlueSMIRF, then when that was discontinued, the Adafruit Bluefruit LE UART Friend https://www.adafruit.com/product/2479.
To save power we use the Qwiic bus to power the BT modules. It’s not ideal, but it works. We’re streaming data and doing file downloads via Bluetooth to a nearby RPi.