Equally confusing and often misunderstood is that the latest version of a compose file should not have a version field at all! It is a blend of v2, v3 and any

Equally confusing and often misunderstood is that the latest version of a compose file should not have a version field at all! It is a blend of v2, v3 and any newly added attributes (v3 some times supported less than v2), that is now called the compose spec. Implementations are supposed to do feature detection based on what attributes are used in the file. Make sure your docker compose is new enough, otherwise it thinks absence of version field means v1!