@container selectors that contain unsupported queries will never select any containers, meaning they will never match. That means this query will never match any container even if there is a size container that will match the width query that would otherwise make the selector match in cases like this: @container (width > 0px) or (unknown) {} This is a recent change to the specification to avoid forward-compatibility issues.
Spec changed for better forward compat. Want to ship change before counter increases: https://chromestatus.com/metrics/feature/timeline/popularity/4596