It's not federated by any means, but if you want to replace FANDOM wikis with other equivalents, Indie Wiki Buddy is a great extension to have on hand.

https://getindie.wiki

There's options to remove FANDOM from search results in favour of other options, and they also allow you to redirect to the Breezewiki frontend for FANDOM to get rid of all those shitty ads and UI, which is legal considering the contents of FANDOM pages are still under the Commons.