I can definitely update the code on the board (verified by changing LED blink rate). I haven't yet tried to see if I can receive data over the USB serial connection.
Environment is macOS 10.15.17, mBed Studio 126.96.36.199, mBed OS 6.10, and using the mbed_os_blinky_example program (with an added printf). I've set the baud rate of the Serial Monitor to 9600, which is what it was set to when things were previously working.
I should add that I also don't see any output when I directly cat the USB serial port.