curl --request GET \
  --url https://discord.com/api/v10/channels/{channel_id}/thread-members/{user_id} \
  --header 'Authorization: <api-key>'

{
  "id": "<string>",
  "user_id": "<string>",
  "join_timestamp": "2023-11-07T05:31:56Z",
  "flags": 123,
  "member": {
    "avatar": "<string>",
    "banner": "<string>",
    "communication_disabled_until": "2023-11-07T05:31:56Z",
    "flags": 123,
    "joined_at": "2023-11-07T05:31:56Z",
    "nick": "<string>",
    "pending": true,
    "premium_since": "2023-11-07T05:31:56Z",
    "roles": [
      "<string>"
    ],
    "user": {
      "id": "<string>",
      "username": "<string>",
      "avatar": "<string>",
      "discriminator": "<string>",
      "public_flags": 123,
      "flags": 0,
      "global_name": "<string>",
      "primary_guild": "<unknown>",
      "bot": true,
      "system": true,
      "banner": "<string>",
      "accent_color": 123,
      "avatar_decoration_data": "<unknown>",
      "collectibles": "<unknown>"
    },
    "mute": true,
    "deaf": true,
    "avatar_decoration_data": "<unknown>",
    "collectibles": "<unknown>"
  }
}