A user should be able to interact with every other user if both wish to.
No I think you've been misled as to how this place works or have misinterpreted information you've recieved. This statement seems to imply that the Fediverse is some sort of free speech haven where people can do whatever they want and say whatever they want, when that couldn't be further from the truth.
The Fediverse is not some decentralized free-speech network where servers work together to thwart censorship and user freedom is paramount (seen plenty of articles and videos claiming this or at the very least implying it).
The Fediverse is a collection of individually run websites which run a software using a decentralized ptotocol to talk to each other. These websites are individually run either by individual people, organizations, or companies, each instance on it's own is not that fundamentally different to classic social media, but the fact that they can communicate with each other in a decentralized manner is what makes it unique and also more powerful. However it's important not to forget the fact that each one of these sites are owned and operated independently and it is the choice of those site owners whether to federate or not with certain instances or ban users from participating or appearing in their instance.
The decentralized or user choice aspect is that a user on an instance that has defederated or banned them, can simply go to another instance that they think fits them better, or they can host their own and call the shots themselves (within reason).
Some people may not like this top down moderation system, but in all honesty it's the only method that really works. True free speech sites are horrible to be on because the loudest and most angry people rule those places and attack anyone who even slightly disagrees with them (look at 4chan and kiwifarms), that mentality hurts the appeal of a space, and so people gravitate away from spaces like that and towards spaces which exclude such content and have rules and some amount of censorship.