"Stackk is a decentralized and federated social network"
Decentralized != federated. P2P != hub-and-spoke.
The two are similar in that there is not a single server. That's all.
Decentralized in governance and federated in data layer. It's specified in the slides and the whitepaper.
There's no extra value with it since someone still has to pin thr files but comes with lots of limitations. You can't run a livestream with IPFS for example