Does anyone know whether it’s possible to use MOSI/MISO or SCK as GPIO pins?

If you don’t need LoRa function during the GPIO time…

Just set the CS pin keep HIGH, and you can Config the MISO/MOSI like this:
pinMode(MISO, OUTPUT);

If you need those pins work back as SPI pin, you need reinit the SPI again.

I already tried:
pinMode(MISO, OUTPUT);
and got the error message:
‘MISO’ was not declared in this scope .

However, your answer suggests that the MISO and MOSI pins are used internally for some other function. Is this correct?