Yes, they tread different paths. RedHat sells support (RedHat Enterprise Linux), develops enterprise ready software and gives unbranded, not supported versions to the community to play with and use it.

GitLab sells SaaS, provides a free self-installable community supported version, and accepts contributions from community.

They're pivoting to a more closed model, which I don't like, but it's still possible to get the community version, the code and play with it.

All in all I think many possible different ways to monetize an free and open source project. They work differently than we get used to over the last century, but it's possible.