Lost serial port on a pico

[CrabbyPete]

I have been writing code in micropython on Pico and all was well, then one time the Thonny said there was no port. I reloaded micro python on the Pico, rebooted and when I looked at the ports on my mac (/dev/cu*) the serial port was no longer there. I plugged into my Windows machine, and still no serial port. I then loaded circuit python on it and the serial port appeared again. If I put micropython on it , no port. I want to use micropython for the threading. Any advice or help would be appreciated.