SPI between Master arduino and Slave arduino
Feel free to take a look at my YouTube videos. They are not monetized so I'm not self-promoting. You can even skip the videos and checkout my GitHub repo with the Master and Slave sketches.
https://youtu.be/A9oSX_dwJKQ
https://youtu.be/PSUzhCtNRRQ
https://github.com/linhartr22/Arduino_SPI_Master_Slave_Demo