I assume you meant 2.x; Compose 2.x is only ~4 months old. I believe the intention of the Podman team is to abandon their podman-compose and work on compatibility with docker-compose 2.x going forward.
The version of the file format is different to the version of the CLI tool. Compose (the file format) 3.x was introduced with Compose (the tool) version 1.10 in 2017: https://github.com/docker/compose/releases/tag/1.10.0
Oh. I was only talking about the program and the interface it uses with the underlying runtime. Compose 2.x expects the underlying tool to have a different API.