@evaristus Federated timelines are usually improved by you muting the whole instance. There are only a gew instances that show porn so its easy to block it all in one go.
But generally we dont silence instances at the server level unless they engage in harassment.
Go to the profile of a user from the server you wush to mute (click their username). Then press the three dots next to their profile. It should have an option saying "Hide everything from <server name>"