c3os supports Rasperry Pi model 3 and 4 with 64bit architecture.
You can find arm64 raspberry images in the releases page. For example https://github.com/c3os-io/c3os/releases/download/v1.21.4-35/c3os-opensuse-arm-rpi-v1.21.4-35.img.tar.xz.
Flash the image into a SD card with dd or Etcher and place your cloud-init configuration file inside the cloud-config directory ( create it if not present ) into the COS_PERSISTENT partition, for example cloud-config/cloud-init.yaml.