This is no longer needed - Linuxserver's calibre image has an arm64 build and so can be used instead: https://docs.linuxserver.io/images/docker-calibre/
This Dockerfile builds Calibre within a Docker container on the Raspberry Pi
Install Docker on the Pi with:
curl -sSL https://get.docker.com | sh
(see https://www.raspberrypi.org/blog/docker-comes-to-raspberry-pi/)
Build the image with:
docker build . -t calibre
This takes a long while; especially on the setup.py bdist_wheel for lxml step.
To run a recipe, and output the resulting file to ~/pi/calibre:
docker run -v /home/pi/calibre:/calibre calibre-docker ebook-convert recipefile.recipe /calibre/outfile.epub
Note the ouput file path is the path within the Docker container. This is mounted on /home/pi/calibre on the Pi's actual filesystem. This path must be absolute and not relative.