I just made a fix to my bb_epaper library to make it easier to support random #Linux SBCs. I added the ability to specify a GPIO "Chip number" other than the default of 0. On the Radxa Rock Pi 4B+, the connections needed to control many display "HATs" are on chip #4. Here's the C++ example code used to generate the photo:

https://github.com/bitbank2/bb_epaper/tree/main/rpi/examples/hello_epaper