Indeed, it seems defective. I tried other ESP32-C6 modules and their GPIO21 behave as expected.

Hi, I have a problem with a brand new, never before used Seeed Xiao ESP32-C6. I tried to establish a SPI connection with an Atmega2560 (level converter in between) and I had no luck. I tried all different SPI modes and speeds down to 250kHz. Nothing. Then I tested every single SPI pin: changing the ...