K3s (and k8s for that matter) expect you to build a hierarchy of yaml configs, mostly because spinning up docker instances will be done in groups with certains traits applying to whole organization, certain ones applying only to most groups, but not all, and certain configs being special for certain services (http nodes added when demand is higher than x threshold).

But I wonder why you want to cluster navidrome or pihole? Navidrome would require a significant load before service load balancing is required (and non-trivial to implement), and pihole can be put behind a round-robin DNS forwarder, and also be weird to implement behind load balancing.