For this part of the setup to upload sketches to the BiBoard, I'm having trouble finding the location of the sdkconfig.h file. I'm on a Mac, and have downloaded the 1.8.19 version of the Arduino IDE. I've been able to configure the environment as detailed in section 3.2.1 in the documentation. I see that there is a sdkconfig.h file in the OpenCatESP32 repository, but I assume this isn't the file that needs to be modified, as it already has this line at the end of the file.
/Users/{yourUserName}/Library/Arduino15/packages/esp32/hardware/esp32/2.0.12/tools/sdk/esp32/qio_qspi
The Library is a hidden directory; you can use Shift+Cmd+. to show it.