If you want to see the console output in a Linux terminal, you can use the following command:

screen /dev/ttyACM0 115200

This is because it seems like the output console is bound to that serial port, so can’t be used for standard serial I/O. There appear to be libraries that could provide serial mirroring/pass-through, and would create a ttyACM1 that could be used for standard serial I/O, but I haven’t tried those.