(Does Podman even have its own implementation of the Compose spec?)
Yes, podman-compose, which is a separate software, …
But the message says podman-compose with a hyphen, a command that does not seem to exist.
… which needs to be installed separately. Don't know whether it works on Mac OS!
External Compose provider
The podman compose (without hyphen) command is Podman’s thin wrapper around any configured external Compose provider.
Currently Podman & Podman Desktop rely upon Docker Compose as an external Compose provider.
The podman-compose (notice hyphen) project is designed to be another external Compose provider, an alternative to using Docker Compose with Podman.
To switch external Compose providers, set PODMAN_COMPOSE_PROVIDER variable, or edit containers.conf. See documentation.
The console message you report does not indicate a problem. To disable the appearance of that console message, set PODMAN_COMPOSE_WARNING_LOGS variable to false, or edit containers.conf. See documentation.
