I’ve learned a lot since I first posted lol! So first I started filtering my front page by “all” instead of Local, which will then show other instances. To subscribe and post to another instance’s community, you can search !communityname@lemmy.ml in your instance’s search to subscribe and post. It seems difficult and clunky to me to discover and subscribe to other communities, unless someone has an easier way? But to answer your question, AFAIK, yes lemmy.world’s meme community is entirely separate from lemmy.ml’s, but you can still subscribe and post to either one.