Due to recent changes in the user-data schema, the ssh_authorized_keys requires a minimum of 1 item, if the attribute is given, see: https://github.com/canonical/cloud-init/blob/main/cloudinit/config/schemas/schema-cloud-config-v1.json#L272

This conflicts with an empty array, which is set here if no keys are configured for the specific system-to-be-installed - see here: https://github.com/theforeman/foreman/blob/develop/app/views/unattended/provisioning_templates/user_data/preseed_autoinstall_cloud_init.erb#L59

Also "lock-passwd" (here: https://github.com/theforeman/foreman/blob/develop/app/views/unattended/provisioning_templates/user_data/preseed_autoinstall_cloud_init.erb#L50) should be changed to "lock_passwd", because the first one is deprecated (see here: https://github.com/canonical/cloud-init/blob/main/cloudinit/config/schemas/schema-cloud-config-v1.json#L208).

I modified both in a copied template and only with these changes i could succesfully install an Ubuntu 22.04.3