No drive is mounted after I flash MicroPython on to my board That is the correct behaviour. On the ESP32, MicroPython presents itself as a serial port, not as a mounted USB... micropython
Sometimes I get an OS error when copying CircuitPython UF2 firmware onto my board There is a known issue where the firmware is copied and then the board reboots itself before your OS thinks... circuitpython micropython
What tools can I use to access the MicroPython REPL and copy code over? The official tool for working with MicroPython is called mpremote. It’s made and maintained by the MicroPython developers, and works... circuitpython micropython