SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    10985, 10986, 10987, 10988, 10989, 10990, 
    10991, 10992, 10993, 10994, 10995, 
    10996, 10997, 10998, 10999, 11000, 
    11001, 11002, 11003, 11004
  ) 
  AND feature_id IN (553, 624, 623) 
  AND lang_code = 'en'

Query time 0.00275

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "14.02"
    },
    "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",
      "used_key_parts": [
        "product_id",
        "feature_id",
        "lang_code"
      ],
      "key_length": "12",
      "rows_examined_per_scan": 60,
      "rows_produced_per_join": 60,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "8.02",
        "eval_cost": "6.00",
        "prefix_cost": "14.02",
        "data_read_per_join": "46K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`gaseus`.`cscart_product_features_values`.`product_id` in (10985,10986,10987,10988,10989,10990,10991,10992,10993,10994,10995,10996,10997,10998,10999,11000,11001,11002,11003,11004)) and (`gaseus`.`cscart_product_features_values`.`feature_id` in (553,624,623)) and (`gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id feature_id variant_id
10985 553 1324
10985 623 1983
10985 624 1705
10986 553 1324
10986 623 2095
10986 624 1705
10987 553 1324
10987 623 2096
10987 624 1705
10988 553 1324
10988 623 2097
10988 624 1705
10989 553 1324
10989 623 2085
10989 624 1705
10990 553 1324
10990 623 2086
10990 624 1705
10991 553 1324
10991 623 2087
10991 624 1705
10992 553 1324
10992 623 2088
10992 624 1705
10993 553 1324
10993 623 2089
10993 624 1705
10994 553 1324
10994 623 2090
10994 624 1705
10995 553 2197
10995 623 1983
10995 624 1705
10996 553 2197
10996 623 2095
10996 624 1705
10997 553 2197
10997 623 2096
10997 624 1705
10998 553 2197
10998 623 2097
10998 624 1705
10999 553 2197
10999 623 2085
10999 624 1705
11000 553 2197
11000 623 2086
11000 624 1705
11001 553 2197
11001 623 2087
11001 624 1705
11002 553 2197
11002 623 2088
11002 624 1705
11003 553 2197
11003 623 2089
11003 624 1705
11004 553 2197
11004 623 2090
11004 624 1705