Don't talk about the high concept of federation, talk about the community that the different services offer.

The classic misstake is to oversell and miss the point that the other party is focusing on.

Don't: "Lemmy is so awesome, it can't be shut down, it is federated, you can even run your own instance and have total control"

What the other party hears: "Lemmy is awesome, and you have to do a lot of stuff to join."

Do: "Hey, have you heard about Lemmy? It is a Reddit clone with a much calmer community, I have had a lot of interesting conversations over there"

This puts the focus on the community rather than the service, people join social networks for the interaction, not the tech.