Copying my comment from the cross-post. Anyone here know enough about ActivityPub to know how much work it will be to make it interoperate nicely with Lemmy in addition to Mastodon?

Looks like it's still a WIP. lemmy.world says that it can't find the user, but my instance shows his profile:

https://midwest.social/u/dansup@loops.video

If you click on the full username, you get redirect to this page, which is the raw ActivityPub profile:

https://loops.video/ap/user/1

{
  "@context": [
    "https://w3id.org/security/v1",
    "https://www.w3.org/ns/activitystreams",
    {
      "toot": "http://joinmastodon.org/ns",
      "manuallyApprovesFollowers": "as:manuallyApprovesFollowers",
      "indexable": "toot:indexable"
    }
  ],
  "id": "https://loops.video/ap/user/1",
  "type": "Person",
  "following": "https://loops.video/ap/user/1/following",
  "followers": "https://loops.video/ap/user/1/followers",
  "inbox": "https://loops.video/ap/user/1/inbox",
  "outbox": "https://loops.video/ap/user/1/outbox",
  "preferredUsername": "dansup",
  "name": "dansup",
  "summary": "",
  "url": "https://loops.video/@dansup",
  "manuallyApprovesFollowers": true,
  "indexable": false,
  "published": "2024-06-06T10:30:00+00:00",
  "publicKey": {
    "id": "https://loops.video/ap/user/1#main-key",
    "owner": "https://loops.video/ap/user/1",
    "publicKeyPem": "-----BEGIN PUBLIC KEY-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA1zzC7XBF81lhJV1o47AA\n9JgguOxygANanxzRUaGOA7BUC9kAWbXI2CoQtzVBTGRiSaiy84d8UgdKQOiAT49m\nmmPdkdnb7zeL7PUKVucv5ppxL5pjXvx11FfYDOIvy52TxjirDIEhvSCiau3BSYf7\nvXtIgsoGnVTkDaStoDauDMfEPGnf6E7eCWHKPOkbeuxF3B3k/Mz2qEmg2MXxegt/\njE4Y75E0BiPs+GeCcYBwri6QddGlQlfveUmj5ZGN2AZGaZdZBNE4FlvJK14GIiTi\n/xT1rYJgwEViFSvGdqXXeRWcWth6UzyzzQrUARLniAf9xcFyYFdx6oJmI3Mu4EWd\nMwIDAQAB\n-----END PUBLIC KEY-----\n"
  },
  "icon": {
    "type": "Image",
    "mediaType": "image/jpeg",
    "url": "https://loopsusercontent.com/avatars/1/v0.jpg"
  }
}

Based on the mention of toots and mastodon, I'm guessing he's focusing on that first. Hopefully interoperability with Lemmy will come quickly though. Being able to embed loops as posts would be really nice.