I fixed it.
The problem comes from serial cable, change another serial cable, use terminal no problem at all.
I'm running into the exact same problem but am wondering which serial cable you used to be able to send commands?
I'm using this one and have the issue of read-only access:
I also tried this pin-out on a different cable, but it does not work either... I don't even see anything on the terminal actually (using screen or minicom):