How do posts end up in World/Uncategorized?

[bboctt]

Hi everyone! With, I have to admit, invaluable help from one of the co-founders, yesterday I was finally able to complete configuration of the ActivityPub feature on my own NodeBB instance, and I'm now obviously trying and testing. I've read the few docs that are currently available on the Fediverse features, but I'm pretty confused on the World section, or Uncategorized category.

I see how, on this instance (community.nodebb.org), that section is filled with many posts coming from many Fediverse instances. Totally random content, that doesn't mention this site or its users in any way, just like you could see on the "Global Timeline" of a software like Mastodon. On my instance, by contrast, no new posts arrive there, although in /admin/settings/activitypub it says the server knows 10 other instances (and growing).

To be more specific, the category itself seems to work, and posts from the Fediverse can appear there, if they are either tagging one of the users of the forum, or posted from Lemmy inside the (broken, but that's an issue for another day) community generated from a forum category. Follow relationships don't seem to influence this at all: even if I follow a Fediverse account from the forum, and they follow my account on the forum, if they post something normally then it won't show up.

I'm not sure if this is a bug, or if again a configuration error on my end. But inside NodeBB I don't see any option that could be tweaked, so who knows. However, I've noticed that some errors related to ActivityPub tend to appear when I run the server with ./nodebb --dev start, below is a sample snippet. Maybe they are related?

[api] Exception caught, error with stack trace follows:
TypeError [ERR_INVALID_URL]: Invalid URL
    at new NodeError (node:internal/errors:405:5)
    at new URL (node:internal/url:676:13)
    at inbox.delete (/Main/Server/SpaccBBS-NodeBB/src/activitypub/inbox.js:155:25)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async Controller.postInbox (/Main/Server/SpaccBBS-NodeBB/src/controllers/activitypub/index.js:124:3)[api] Exception caught, error with stack trace follows:
TypeError [ERR_INVALID_URL]: Invalid URL
    at new NodeError (node:internal/errors:405:5)
    at new URL (node:internal/url:676:13)
    at inbox.delete (/Main/Server/SpaccBBS-NodeBB/src/activitypub/inbox.js:155:25)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async Controller.postInbox (/Main/Server/SpaccBBS-NodeBB/src/controllers/activitypub/index.js:124:3)2024-07-27T11:29:22.594Z [4567/190136] - verbose: [activitypub/get] Received 410 when querying https://social.vivaldi.net/users/helloleo2024#main-key
2024-07-27T11:29:22.594Z [4567/190136] - verbose: [activitypub/get] Error received: Gone
2024-07-27T11:29:44.906Z [4567/190136] - verbose: [activitypub/get] Received 410 when querying https://mastodon.social/users/fmhgshkj101#main-key
2024-07-27T11:29:44.907Z [4567/190136] - verbose: [activitypub/get] Error received: Gone
[api] Exception caught, error with stack trace follows:
TypeError [ERR_INVALID_URL]: Invalid URL
    at new NodeError (node:internal/errors:405:5)
    at new URL (node:internal/url:676:13)
    at inbox.delete (/Main/Server/SpaccBBS-NodeBB/src/activitypub/inbox.js:155:25)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async Controller.postInbox (/Main/Server/SpaccBBS-NodeBB/src/controllers/activitypub/index.js:124:3)

It could be that I'm missing something, considering also how the World section here doesn't show up every possible post in the Fediverse, otherwise after scrolling a few dozen entries we would see posts created just a few minutes ago, and not hours or days before; it would be a huge spam like we see on the official Mastodon instances, or any other big one. Maybe posts appear in World only after they have X number of comments? Or maybe an admin must boost them? How? I'm really lost..