I saved my updated code in Mu but nothing happened?
Try hitting the reset button on your Breadstick, it's the button closest to the USB-C port.
My Breadstick isn't showing up as a CircuitPy drive, it shows up as a USB mass storage device?
Sometimes the flash memory chip can get corrupted, it just needs to be nuked.
Wipe the flash via CircuitPython REPL commands
Launch Mu and open the serial window. Click into the serial window and type Ctrl-C to send a keyboard interrup to the program currently running on your Breadstick, then press any key to enter REPL mode, the LEDs on your Breadstick will turn white. Inside the REPL, send the following lines of Python code. WARNING - this will overwrite your code.py to with a simple "Hello World" program.
import storage
storage.erase_filesystem()
More Info:
Wipe the flash via DFU mode and Raspberry Pi Foundations nuke.uf2 file
While holding down the Boot button, click the Reset button to boot into DFU mode. Copy the Raspberry Pi Foundation's nuke.uf2 file into the RPI-RP2 drive.