The MAX7219 chip uses a simple serial protocol at any speed up to 10MHz. This C code implements the protocol for the Raspberry Pico. It can update an 8-character display at several kHz. Rewriting it to use the Pico’s PIO should make it much faster - the MAX7219 should be able to update at 62 KHz. Of course, this is far faster than human perception, but offloading the bit-banging to the PIO would let the processor handle real-time tasks better.