You can download the prebuilded image from https://hub.docker.com/r/mathosk/rpi-ruby-3.1.2-ubuntu-aarch64
Or build it on your Raspberry Pi by: sudo docker build -t mathosk/rpi-ruby-3.1.2-ubuntu-aarch64:latest .
Matho/rpi-ruby-3.1.2-ubuntu-aarch64
Docker image source code for Raspberry Pi aarch64 and Ruby 3.1.2
Dockerfile