Sandbox

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 = 'ar' 
  AND gp.group_id IN (13, 14, 16, 17, 18, 19, 20, 21, 6, 3)

Query time 0.00066

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "32.41"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "gp",
          "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": 26,
          "rows_produced_per_join": 26,
          "filtered": "100.00",
          "index_condition": "(`betaatif_store`.`gp`.`group_id` in (13,14,16,17,18,19,20,21,6,3))",
          "cost_info": {
            "read_cost": "11.61",
            "eval_cost": "2.60",
            "prefix_cost": "14.21",
            "data_read_per_join": "416"
          },
          "used_columns": [
            "product_id",
            "group_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "gpf",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "idx_group_id"
          ],
          "key": "idx_group_id",
          "used_key_parts": [
            "group_id"
          ],
          "key_length": "3",
          "ref": [
            "betaatif_store.gp.group_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 26,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "6.50",
            "eval_cost": "2.60",
            "prefix_cost": "23.31",
            "data_read_per_join": "2K"
          },
          "used_columns": [
            "feature_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": [
            "betaatif_store.gpf.feature_id",
            "betaatif_store.gp.product_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 26,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "6.50",
            "eval_cost": "2.60",
            "prefix_cost": "32.41",
            "data_read_per_join": "20K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id",
            "lang_code"
          ]
        }
      }
    ]
  }
}

Result

feature_id	product_id	variant_id	group_id
2	124	12	3
2	378	8	3
2	379	9	3
2	391	8	6
2	394	9	6
2	393	12	6
2	415	6	13
2	449	7	13
2	417	9	13
2	418	6	14
2	448	7	14
2	420	9	14
2	424	6	16
2	447	7	16
2	426	9	16
2	427	6	17
2	446	7	17
2	429	9	17
2	430	6	18
2	445	7	18
2	432	9	18
2	433	6	19
2	444	7	19
2	435	9	19
2	436	6	20
2	443	7	20
2	438	9	20
2	439	6	21
2	442	7	21
2	441	9	21

feature_id	product_id	variant_id	group_id
2	124	12	3
2	378	8	3
2	379	9	3
2	391	8	6
2	394	9	6
2	393	12	6
2	415	6	13
2	449	7	13
2	417	9	13
2	418	6	14
2	448	7	14
2	420	9	14
2	424	6	16
2	447	7	16
2	426	9	16
2	427	6	17
2	446	7	17
2	429	9	17
2	430	6	18
2	445	7	18
2	432	9	18
2	433	6	19
2	444	7	19
2	435	9	19
2	436	6	20
2	443	7	20
2	438	9	20
2	439	6	21
2	442	7	21
2	441	9	21

feature_id	product_id	variant_id	group_id
2	124	12	3
2	378	8	3
2	379	9	3
2	391	8	6
2	394	9	6
2	393	12	6
2	415	6	13
2	449	7	13
2	417	9	13
2	418	6	14
2	448	7	14
2	420	9	14
2	424	6	16
2	447	7	16
2	426	9	16
2	427	6	17
2	446	7	17
2	429	9	17
2	430	6	18
2	445	7	18
2	432	9	18
2	433	6	19
2	444	7	19
2	435	9	19
2	436	6	20
2	443	7	20
2	438	9	20
2	439	6	21
2	442	7	21
2	441	9	21

feature_id	product_id	variant_id	group_id
2	124	12	3
2	378	8	3
2	379	9	3
2	391	8	6
2	394	9	6
2	393	12	6
2	415	6	13
2	449	7	13
2	417	9	13
2	418	6	14
2	448	7	14
2	420	9	14
2	424	6	16
2	447	7	16
2	426	9	16
2	427	6	17
2	446	7	17
2	429	9	17
2	430	6	18
2	445	7	18
2	432	9	18
2	433	6	19
2	444	7	19
2	435	9	19
2	436	6	20
2	443	7	20
2	438	9	20
2	439	6	21
2	442	7	21
2	441	9	21