SELECT 
  pfv.feature_id, 
  pfv.product_id, 
  pfv.variant_id, 
  gp.group_id 
FROM 
  cscart_product_features_values AS pfv 
  INNER JOIN cscart_product_variation_group_products AS gp ON pfv.product_id = gp.product_id 
  INNER JOIN cscart_product_variation_group_features AS gpf ON gpf.group_id = gp.group_id 
  AND gpf.feature_id = pfv.feature_id 
WHERE 
  pfv.lang_code = 'en' 
  AND gp.group_id IN (
    807, 469, 308, 381, 279, 287, 318, 470, 
    212, 266
  )

Query time 0.00093

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "30.56"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "gpf",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "idx_group_id"
          ],
          "key": "idx_group_id",
          "used_key_parts": [
            "group_id"
          ],
          "key_length": "3",
          "rows_examined_per_scan": 11,
          "rows_produced_per_join": 11,
          "filtered": "100.00",
          "index_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`gpf`.`group_id` in (807,469,308,381,279,287,318,470,212,266))",
          "cost_info": {
            "read_cost": "6.36",
            "eval_cost": "1.10",
            "prefix_cost": "7.46",
            "data_read_per_join": "1K"
          },
          "used_columns": [
            "feature_id",
            "group_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "gp",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "idx_group_id"
          ],
          "key": "idx_group_id",
          "used_key_parts": [
            "group_id"
          ],
          "key_length": "3",
          "ref": [
            "softwarepirmam_hewadelivard_cscart_4.gpf.group_id"
          ],
          "rows_examined_per_scan": 3,
          "rows_produced_per_join": 33,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "8.25",
            "eval_cost": "3.30",
            "prefix_cost": "19.01",
            "data_read_per_join": "528"
          },
          "used_columns": [
            "product_id",
            "group_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "pfv",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "fpl",
          "used_key_parts": [
            "feature_id",
            "product_id",
            "lang_code"
          ],
          "key_length": "12",
          "ref": [
            "softwarepirmam_hewadelivard_cscart_4.gpf.feature_id",
            "softwarepirmam_hewadelivard_cscart_4.gp.product_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 33,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "8.25",
            "eval_cost": "3.30",
            "prefix_cost": "30.56",
            "data_read_per_join": "25K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id",
            "lang_code"
          ]
        }
      }
    ]
  }
}

Result

feature_id product_id variant_id group_id
656 2522 1560 212
656 2719 1600 266
656 2728 2993 266
656 2792 1600 279
656 2793 1560 279
656 2794 1607 279
656 2802 1560 287
656 2836 1559 287
656 2934 1560 308
656 2935 1559 308
656 2936 1682 308
656 2937 1558 308
656 3021 1560 318
656 3022 1559 318
656 3377 1559 381
656 3378 1560 381
656 4119 1560 469
656 4120 1560 469
656 4121 1560 469
656 4122 1560 469
656 4123 1560 469
648 4119 1686 469
648 4120 1561 469
648 4121 1562 469
648 4122 1563 469
648 4123 1687 469
656 3373 1558 470
656 4124 1559 470
656 4125 1600 470
766 8474 8557 807
766 8475 8558 807
766 2441 8553 807