Decentralization in this case means one can secede easily from the central authority. So anyone working on a project can easily split away from the main group at any time. But every project have a clear governance where the main direction is set and the canonical version of the thing being under version control is stored.

That canonical version is altered following a process and almost every project agrees that changes should be proposed against it. Even with independent agents, there should be a way to ensure consensus and decides the final version. And that problem is a very hard one.

And yet after all these year of git supporting no source of truth we still fall back on it. As long as you have an authoritative version and authoritative release then you have one source of truth. Linus imagined everyone contributing with no central authority and yet we look to GitHub and Gitlab to centralize our code. Git is already decentralized and generally we find it impractical.