Hit there,
Try
8,9,10… On Xiao.
pinMode(D6, INPUT_PULLUP); // /WP
pinMode(D7, INPUT_PULLUP); // /HOLD
pinMode(SS_SPI0, OUTPUT); // CS for flash
digitalWrite(SS_SPI0, HIGH); // <-- Set CS pin HIGH to deselect
Serial.println("--------------"); Check what it thinks they are.
Serial.println(SS_SPI0);
Serial.println(MOSI); // master out, slave in
Serial.println(MISO); // master in, slave out
Serial.println(SCK); // clock
Serial.println("--------------");
HTH
GL PJ