I do not know how to set it in the code. However, I had more luck today in my searches and found a post saying that the main xtal may be at 26MHz instead of 40MHz. I changed this in the configuration and the magic happened, the log is now readable! Any way thanks for you replay and maybe this can he...

It is left as in the sample, not specified.
Do you know where I can specify it ?

Running blink_example on ESP8684-DevKitM-1 (target esp32-C2) does not display correct output. I've tryed to change uart speed with idf.py monitor -b 115200 without success. So I switched to another board based on ESP32 (ESP32-WROOM-32E); build and load the same code. Result I can see the log. Could ...