They might be rare, but they do exist: https://en.wikipedia.org/wiki/Igalia

Igalia is very serious about worker ownership. They aren't legally structured as a cooperative, as they don't technically meet the definition - as I understand it, they were nervous about the idea of committing wholly to new employees getting an equal vote right away, so there is a longer, more gradual process through which employees become owners and gain voting rights. But a very large fraction have them, and (like a cooperative) their rights are legally enforceable.