There are countless Wikipedia forks. To a first approximation, they all suck.
The Spanish Wikipedia had a considerable mutiny around 2011, when all admins quit en masse and moved to their own fork, but looks like they gave up the ghost around 2016:
The only successful wiki fork I'm aware of is Wikivoyage (a Wikimedia project) from Wikitravel, which was bought by a company that proceeded to cram it full of monkey punch ads and alienate its entire userbase.
It would need software to support governance by the volunteers who actually maintain it, rather than what exists now.
These "benevolent dictatorships" all devolve into regular dictatorships after the benevolent dictator leaves (or finds a new partner who promises to make them rich), and the ivy MBAs show up with top tier salary expectations and a vision for what to do with the brand that has little or no relationship with what the brand became successful doing.
It's of course a collective action problem. The reason that wikipedia can be plundered for cash (such a precious thing, so much management risk) is the same reason Elsevier and others can collect billions on the backs of unpaid researchers and reviewers.
I would be happy to make a donation to it and have the original wmf rot.