Hash them with the post ID appended, so a user can’t be identified across posts

There are multiple similar subs on reddit as well though, often with very slightly different names

https://lemmy.fediverse.observer/map

If they look at the “all” feed they’ll see 90% of the same stuff from 90% of instances.

Once (from experience) they learn what they want from an instance, they can always switch.

“Here’s Lemmy. It’s like Reddit. There’s a bunch of different websites for it, but they all have basically the same people and posts on them. Just join one near you, if you don’t like it you can always use a different one later”

They don’t really need to know about that until they have had time on Lemmy to hear about what those defederated instances actually do