SELECT 
  f.feature_id, 
  f.purpose, 
  p.product_id, 
  p.parent_product_id, 
  g.id, 
  g.code 
FROM 
  cscart_product_variation_group_features AS f 
  INNER JOIN cscart_product_variation_groups AS g ON f.group_id = g.id 
  INNER JOIN cscart_product_variation_group_products AS p ON f.group_id = p.group_id 
WHERE 
  p.product_id IN (
    20718, 20723, 20293, 20294, 20295, 20719, 
    20561, 20562, 20564, 20563, 20692, 
    20731, 20732, 20733, 20465, 20466, 
    20548, 20549, 20419, 20739, 20738, 
    20725, 20737, 20552
  )

Query time 0.00091

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "f",
      "access_type": "ALL",
      "possible_keys": ["idx_group_id"],
      "rows": 6,
      "filtered": 100
    },
    "table": {
      "table_name": "g",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["id"],
      "ref": ["admin_test.f.group_id"],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "p",
      "access_type": "ALL",
      "possible_keys": ["PRIMARY", "idx_group_id"],
      "rows": 15,
      "filtered": 80,
      "attached_condition": "p.group_id = f.group_id and p.product_id in (20718,20723,20293,20294,20295,20719,20561,20562,20564,20563,20692,20731,20732,20733,20465,20466,20548,20549,20419,20739,20738,20725,20737,20552)"
    }
  }
}