ActivityPub and Mastodon brought new incentives into the world of decentralised communication platforms, even so far as I would call it a serious alternative to platforms like Twitter. But all efforts made by hundreds of individuals every day – administrating servers, developing software and moderating communities – have a weak spot which needs to be addressed in the near future: who has control over the underlying computing infrastructure of the Fediverse? And are users aware of the conditions?
Free software is heavily correlated to privacy yes. And the Fediverse pretty much entirely free software. However, the technical aspect of federation has little to do with privacy. A free software centralised social network could be pretty private, even more than the Fediverse , because the data is not shared with multiple hosts. And the other way works too. You could build a federated social network that is significantly less private than the Fediverse currently is.
Also, the Fediverse can only be considered private to the extent that there are no advertising trackers on the platforms. However, pretty much every post on the Fediverse can be viewed by anyone.