• Poll this endpoint and check the new_entries node, https://fantasy.premierleague.com/api/leagues-classic/31936/standings/
• Notify about new entries: 🎉 John joined the YOLO league!

{
  "new_entries": {
    "results": [
      {
        "entry": 700843,
        "entry_name": "Takk for meg",
        "joined_time": "2021-11-30T11:25:06.956253Z",
        "player_first_name": "John",
        "player_last_name": "Korsnes"
      }]
  },
  "league": {
    "league_type": "s", //  [s|x]. s: created by FPL. x: created by end-users?
  },
}

It looks like all the larger leagues like overall, nations, broadcasters leagues, gameweek leagues etc (1-314, + broadcaster ids) are of league_type:s and always contain empty results for new_entries. league_type:x have results for new entries.