You need to follow people for their posts to federate to your server. Posts won't federate until you're following a user and they make a post, or boost a post. Also, old posts won't federate unless they are boosted/reblogged/shared. This is also how Mastodon works.
I recommend following as many people as you can, especially people who boost a lot, and following the people who are being boosted.
It takes a lot of effort to start the process up.
Also make sure that the AP and federation features are turned on in the env file, as i believe by default they are off with pixelfed.
Yes, i really wish there was a good way to do pixelfed relaying.