core/homeassistant/components/plex/icons.json

{
  "entity": {
    "sensor": {
      "plex": {
        "default": "mdi:plex"
      }
    }
  },
  "services": {
    "refresh_library": {
      "service": "mdi:refresh"
    },
    "scan_for_clients": {
      "service": "mdi:database-refresh"
    }
  }
}