SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    13198, 13199, 13200, 13201, 13202, 13203, 
    13197
  ) 
  AND feature_id IN (
    637, 636, 647, 646, 623, 622, 626, 553, 
    625, 624, 627, 628, 595
  ) 
  AND lang_code = 'en'

Query time 0.00471

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "6.75"
    },
    "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": "PRIMARY",
      "used_key_parts": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "key_length": "15",
      "rows_examined_per_scan": 16,
      "rows_produced_per_join": 16,
      "filtered": "100.00",
      "using_index_for_skip_scan": true,
      "cost_info": {
        "read_cost": "5.15",
        "eval_cost": "1.60",
        "prefix_cost": "6.75",
        "data_read_per_join": "12K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`test2_gaseus`.`cscart_product_features_values`.`product_id` in (13198,13199,13200,13201,13202,13203,13197)) and (`test2_gaseus`.`cscart_product_features_values`.`feature_id` in (637,636,647,646,623,622,626,553,625,624,627,628,595)) and (`test2_gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id feature_id variant_id
13197 553 1973
13198 553 1973
13199 553 1973
13200 553 1973
13201 553 1973
13202 553 1973
13203 553 1973
13197 595 1904
13198 595 1905
13199 595 1789
13200 595 2499
13201 595 1787
13202 595 1900
13203 595 1899
13197 622 2497
13198 622 2497
13199 622 2497
13200 622 2497
13201 622 2497
13202 622 2497
13203 622 2497
13197 623 2501
13198 623 2501
13199 623 2501
13200 623 2501
13201 623 2501
13202 623 2501
13203 623 2501
13197 624 1803
13198 624 1803
13199 624 1803
13200 624 1803
13201 624 1803
13202 624 1803
13203 624 1803
13197 625 2123
13198 625 2123
13199 625 2123
13200 625 2123
13201 625 2123
13202 625 2123
13203 625 2123
13197 626 1879
13198 626 1879
13199 626 1879
13200 626 1879
13201 626 1879
13202 626 1879
13203 626 1879
13197 627 1659
13198 627 1659
13199 627 1659
13200 627 1659
13201 627 1659
13202 627 1659
13203 627 1659
13197 628 1660
13198 628 1660
13199 628 1660
13200 628 1660
13201 628 1660
13202 628 1660
13203 628 1660
13197 636 2348
13198 636 2348
13199 636 2348
13200 636 2348
13201 636 2348
13202 636 2348
13203 636 2348
13197 637 2345
13198 637 2345
13199 637 2345
13200 637 2345
13201 637 2345
13202 637 2345
13203 637 2345
13197 646 2370
13198 646 2370
13199 646 2370
13200 646 2370
13201 646 2370
13202 646 2370
13203 646 2370
13197 647 2374
13198 647 2374
13199 647 2374
13200 647 2374
13201 647 2374
13202 647 2374
13203 647 2374