MCore(Arduino) - Python bluetooth communication
Probably because you never called bluetooth.open().

What would be much easier to do is use pySerialTransfer and SerialTransfer.h to guarantee reliable and robust serial communication between Python and your Arduino.

pySerialTransfer is pip-installable and cross-platform compatible. SerialTransfer.h runs on the Arduino platform and can be installed through the Arduino IDE's Libraries Manager.

Both of these libraries have highly efficient and robust packetizing/parsing algorithms with easy to use APIs and come with examples.