I am sure that someone has written a simple library for the Waveshare.
From guesswork, all that is needed is to write 8-bit commands and 8-bit parameters with SPI.write16() instead of 8-bit. Writing a 16-bit pixel is done with write16().
I do not own a Waveshare. I do not want to own a Waveshare.
Surely Waveshare provide a library already.
David.