Matrix Max7219 with 2 or 3 or More Design Pictures

https://youtu.be/2rZWN1IcZpA?si=lzkYUDrVhY3a4ZX2

How to use SPI (Serial Peripheral Interface) in Arduino to Communication between two Arduino Boards

https://circuitdigest.com/microcontroller-projects/arduino-spi-communication-tutorial

Connect Two Arduino Boards Using I2C Communication Protocol

https://electropeak.com/learn/connect-two-arduino-boards-using-i2c-communication-protocol/#google_vignette