I've fixed the Apache configuration to properly route requests with Accept: application/activity+json header to the backend, and updated all internal URLs in the database from the internal hostname to the public domain. Now the endpoint returns some JSON as you requested.

$ curl -H 'Accept: application/activity+json' https://лемми.опенсорс.рус/c/rust_rus
{
  "@context": [
    "https://join-lemmy.org/context.json",
    "https://www.w3.org/ns/activitystreams"
  ],
  "type": "Group",
  "id": "https://xn--e1aghfa.xn--e1aqbccjfc.xn--p1acf/c/rust_rus",
  "preferredUsername": "rust_rus",
  "inbox": "https://xn--e1aghfa.xn--e1aqbccjfc.xn--p1acf/c/rust_rus/inbox",
  "followers": "https://xn--e1aghfa.xn--e1aqbccjfc.xn--p1acf/c/rust_rus/followers",
  "publicKey": {
    "id": "https://xn--e1aghfa.xn--e1aqbccjfc.xn--p1acf/c/rust_rus#main-key",
    "owner": "https://xn--e1aghfa.xn--e1aqbccjfc.xn--p1acf/c/rust_rus",
    "publicKeyPem": "-----BEGIN PUBLIC KEY-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAn48V3rPTqtEHHFzKHAVS\njfl593Qy0G4GTXWaIyP0Zuv/lyw90LmKZKe1nnzQ+GDv4glcdjp1RpJ/C/6Yw+91\nuOmvR734mhCa21f7+5tlUnsg1kENbV4oTtFlEBFSBTCjf7uJNNds3UBz7oMQpq0T\nB7+PxSKd1kUZboBDhkWaB3M+etgxos6IAX9Va+YVoHEoB5k+zkZ9PrOViuI3C76R\nAsNoOBmE9ZzhOWb+BT/g7KWuxIULYteUyqbPQH5VYqfcv6/vTrNsMeMhIei6QV+b\nsl4xVX+NRhhrtqGhPMietK1oDhvzvEn0/VV4jjXT8bquMUnoQ3N7Eq3JN35eO/ZK\n0wIDAQAB\n-----END PUBLIC KEY-----\n"
  },
  "name": "Раст (Общение на русском языке)",
  "summary": "<p>Программирование на Rust</p>\n",
  "source": {
    "content": "Программирование на Rust",
    "mediaType": "text/markdown"
  },
  "sensitive": false,
  "attributedTo": "https://xn--e1aghfa.xn--e1aqbccjfc.xn--p1acf/c/rust_rus/moderators",
  "postingRestrictedToMods": false,
  "outbox": "https://xn--e1aghfa.xn--e1aqbccjfc.xn--p1acf/c/rust_rus/outbox",
  "endpoints": {
    "sharedInbox": "https://xn--e1aghfa.xn--e1aqbccjfc.xn--p1acf/inbox"
  },
  "featured": "https://xn--e1aghfa.xn--e1aqbccjfc.xn--p1acf/c/rust_rus/featured",
  "language": [
    {
      "identifier": "ru",
      "name": "Русский"
    }
  ],
  "published": "2026-06-11T18:51:34.786453Z"