I've set up a couple of single-user instances of fediverse apps (Mastodon, Lemmy). With Lemmy, I can post/comment to any community/thread I want that is federated, but I can't seem to do that with Mastodon.

With that being the case, how does the content I post on Mastodon get shown to people on other instances (I know replying works differently). I feel like any top-level post I make on my instance is basically like shouting into the void, correct?

Also, if I were to set up a Pixelfed instance, would I have the same problem where my content doesn't get shown to anyone (except those that follow me?)