If you want to enable the podman auto-update systemd timer on Fedora CoreOS for rootless containers, check out this Butane config below:

variant: fcos
version: 1.5.0
passwd:
  users:
    - name: core
      ssh_authorized_keys:
        - ssh-rsa CHANGEME
    - name: penguin
storage:
  files:
    - path: /var/lib/systemd/linger/penguin
      mode: 0644
    - path: /home/penguin/.config/containers/systemd/hello-world.container
      mode: 0644
      contents:
        inline: |
          [Unit]
          Description=hello-world

          [Container]
          AutoUpdate=registry
          Image=hello-world
          Network=host

          [Install]
          WantedBy=default.target          
      user:
        name: penguin
      group:
        name: penguin
  links:
    - path: /home/penguin/.config/systemd/user/timers.target.wants/podman-auto-update.timer
      target: /usr/lib/systemd/user/podman-auto-update.timer
      hard: false
      user:
        name: penguin
      group:
        name: penguin