There’s an instance lemmit.online that mirrors reddit content and you can subscribe to the communities.
Like others said, there is so much content it’s hard to get conversations going, it works better to cross post interesting content to a lemmy community.
Yes, it’s a lemmy thing that when the first personnel on your instance subscribes, it takes like a page of posts and then only the new ones going forward.
Lemmit.online used to have a way to add new subreddits, but it seems they have stopped accepting new ones. Must have got a bit too big to handle.