I’m very new here but I decided to check and compare the posts in a community on lemmy.world (where I have my account) and that same community on the instance where it resides and the posts were almost all completely different! Is that how it’s supposed to work or are they supposed to be synced? Sorry if this is a noob question, I’m new here
No, communities on different instances will not have the same content. This is one of the features of the fediverse.
Each instance can have it’s own /c/memes and they won’t conflict. So, there could be https://lemmy.world/c/memes and https://lemmyverse.org/c/memes and they could each be different with different content and rules. If you want to see each instances ‘memes’ community, then you will need to subscribe to them individually from your home instance. Once you do that, the ‘memes’ community will be ‘cached’ on your home instance and it will show up in everyone’s feed on your home server.
that’s what I did. I subbed to (for example) memes@lemmy.ml and viewed c/memes directly on lemmy.ml and it had different content
Right now its a bit of a mess while things are quickly developing. Ultimately, federated communities should look the same across the fediverse, with a slight delay.
There are some caveats to that around defederation.
In that case, you should see pretty much the same content. The only reason I could think they would be different is if you are the first one to subscribe to that community on your instance, then not all the posts will show up. You home instance only starts caching a community when someone subscribes to it and you may have been the first. Other than that, I have seen reports of people saying that the posts aren’t the same, but usually it’s a few missing here and there. Same with comments.