SELECT 
  f.feature_id, 
  f.purpose, 
  p.product_id, 
  p.parent_product_id, 
  g.id, 
  g.code 
FROM 
  cscart_product_variation_group_features AS f 
  INNER JOIN cscart_product_variation_groups AS g ON f.group_id = g.id 
  INNER JOIN cscart_product_variation_group_products AS p ON f.group_id = p.group_id 
WHERE 
  p.product_id IN (730, 731, 732)

Query time 0.00019

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "f",
      "access_type": "ALL",
      "possible_keys": ["idx_group_id"],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "g",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["id"],
      "ref": ["multi_vendor.f.group_id"],
      "rows": 1,
      "filtered": 100
    },
    "block-nl-join": {
      "table": {
        "table_name": "p",
        "access_type": "range",
        "possible_keys": ["PRIMARY", "idx_group_id"],
        "key": "PRIMARY",
        "key_length": "3",
        "used_key_parts": ["product_id"],
        "rows": 1,
        "filtered": 100,
        "attached_condition": "p.product_id in (730,731,732)"
      },
      "buffer_type": "flat",
      "buffer_size": "5Kb",
      "join_type": "BNL",
      "attached_condition": "p.group_id = f.group_id"
    }
  }
}