Any update on this? I've tried the same process as @Gaurav-Borade, including the instructions here:
https://docs.modalai.com/usb-expander-and-debug-user-guide/
and I also see nothing listed under sudo fastboot devices.
Using the usb-expander-and-debug-user-guide I'm able to start a screen to /dev/ttyUSB0, but I can't get adb shell to work after the screen is started.
I'm on Ubuntu Linux 18.04, I'll switch to another Ubuntu 18.04 machine and re-run the debricking procedure to see if anything changes.