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 (261, 453, 562, 561, 556, 364, 363)

Query time 0.00085

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "19.61"
    },
    "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": 7,
          "rows_produced_per_join": 7,
          "filtered": "100.00",
          "index_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`gpf`.`group_id` in (261,453,562,561,556,364,363))",
          "cost_info": {
            "read_cost": "4.21",
            "eval_cost": "0.70",
            "prefix_cost": "4.91",
            "data_read_per_join": "728"
          },
          "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": 21,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "5.25",
            "eval_cost": "2.10",
            "prefix_cost": "12.26",
            "data_read_per_join": "336"
          },
          "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": 21,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "5.25",
            "eval_cost": "2.10",
            "prefix_cost": "19.61",
            "data_read_per_join": "16K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id",
            "lang_code"
          ]
        }
      }
    ]
  }
}

Result

feature_id product_id variant_id group_id
656 2702 1560 261
656 2703 2993 261
656 3213 1559 363
656 3214 1560 363
656 3216 1560 364
656 3215 1559 364
656 4024 1607 453
656 3649 1560 453
656 4026 2758 453
656 4025 1609 453
656 4944 1559 556
656 4942 1560 556
656 4945 1558 556
656 4959 1559 561
656 4958 1560 561
656 4973 6258 562
656 4972 6257 562
656 4971 6256 562
656 4970 6255 562
656 4969 6254 562
656 4968 6252 562
656 4967 6250 562
656 4966 1914 562
656 4965 1596 562
656 4964 1560 562
656 4963 1556 562
656 4962 6253 562