OK, replying to my own query, the fryefryefrye fellow came back on Github, apparently you have to use an OLDER version of Arduino for the ESP32C3 (note that the newer version of Arduino, v2.3.6 actually worked OK on my ESP32-WROOM).
Whoever is updating the instructions please note; also to @jackjourneyman for the parallel Guide on this topic.
Older Versions of Arduino IDE available here.
I have moved on PlatformIO and not use Arduino any more.
You have a very new Arduino that I have not been used.
I just try to build this project with Arduino 1.8.10 with ESP32C3. It's OK.