SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    35730, 35810, 35811, 35812, 35813, 35814, 
    35815, 35816, 35817, 35818, 35819, 
    35820, 35821, 35822, 35823, 35824, 
    35825, 35826, 35827, 35828, 35829, 
    35830, 35831, 35832, 35833, 35834, 
    35835, 35836, 35837, 35838, 35839, 
    35840, 35841, 35842, 35843
  ) 
  AND feature_id IN (23620, 23621) 
  AND lang_code = 'vi'

Query time 0.00528

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_features_values",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "idx_product_feature_variant_id",
          "key_length": "12",
          "used_key_parts": ["product_id", "feature_id", "lang_code"],
          "rows": 70,
          "filtered": 100,
          "attached_condition": "cscart_product_features_values.product_id in (35730,35810,35811,35812,35813,35814,35815,35816,35817,35818,35819,35820,35821,35822,35823,35824,35825,35826,35827,35828,35829,35830,35831,35832,35833,35834,35835,35836,35837,35838,35839,35840,35841,35842,35843) and cscart_product_features_values.feature_id in (23620,23621) and cscart_product_features_values.lang_code = 'vi'",
          "using_index": true
        }
      }
    ]
  }
}