Does that let you build images on a macOS host that works on Windows and Linux too? It doesn't seem to talk about what platform the images support, only where you could run containers.

Not sure about Windows, but yes to Linux. It runs linux containers (not darwin), plus can have rosetta. And I build multi arch images (arm64/amd64). It uses buildkit, the same Docker uses, so I am sure you can build Windows containers with it as well.

Just a note, I am working for the org, that sells enterprise software shipped as container images, publishes on Docker Hub and RedHat. No issues migrating to apple/container.