indeed, using different ttl-to-usb I managed to flash it. Had to manually
enter load mode (grounding pin 9) and now all is ok.
thanks

after much work, got esp-idf to work on a Mac running Big Sur, and
get the same error. I'm waiting to receive a esp32c3 not from M5 to see
if it has the same issues. BTW, espressif is very silent
bleeding edge of technology :-(

@felmue
thanks for the info, questions:
1- what version of idf
2- what baudrate

i CAN flash all other products as long as it's esp32, this one is esp32c3 and failes:

/vol/src/esp/esp-idf/components/esptool_py/esptool/esptool.py -p /dev/ttyU1 --before default_reset --after hard_reset --chip esp32c3 erase_flash
esptool.py v3.2-dev
Serial port /dev/ttyU1
Connecting...
Failed to get PID of a device on /dev/ttyU1, using standard reset sequence.
......
Chip is ESP32-C3 (revision 3)
Features: Wi-Fi
Crystal is 40MHz
MAC: 7c:df:a1:a3:61:74
Uploading stub...

A fatal error occurred: Failed to write to target RAM (result was 01070000)