SELECT 
  cscart_product_review_prepared_data.product_id AS product_id, 
  cscart_product_review_prepared_data.average_rating AS average_rating, 
  cscart_product_review_prepared_data.reviews_count AS reviews_count 
FROM 
  cscart_product_review_prepared_data 
WHERE 
  cscart_product_review_prepared_data.product_id IN (
    321, 320, 319, 318, 317, 316, 315, 314, 
    313, 312, 311, 310, 309, 308, 307, 306, 
    305, 304, 303, 302
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00030

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_review_prepared_data",
          "access_type": "ALL",
          "possible_keys": ["PRIMARY"],
          "rows": 3,
          "filtered": 100,
          "attached_condition": "cscart_product_review_prepared_data.storefront_id = 0 and cscart_product_review_prepared_data.product_id in (321,320,319,318,317,316,315,314,313,312,311,310,309,308,307,306,305,304,303,302)"
        }
      }
    ]
  }
}