As you can see here, they now recommend this:
val bluetoothManager = context.getSystemService(Context.BLUETOOTH_SERVICE) as BluetoothManager
bluetoothManager.getAdapter()
The reason seems to be that BluetoothAdapter.getDefaultAdapter() ignores Context, while more complex apps might need to explicitly reference the correct Context.
Not a good reason to deprecate it in my opinion, as I can’t think of a realistic/frequent usecase where the BluetoothAdapter needs to be based on the Context. They should have just left both options (Context based and default) in without deprecation.