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 (
    94, 96, 136, 90, 252, 95, 251, 84, 85, 88, 
    47, 253, 138, 93, 87, 139, 83, 256, 137, 
    248, 89, 82
  )

Query time 0.00175

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "g",
          "access_type": "system",
          "possible_keys": ["PRIMARY"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "f",
          "access_type": "ref",
          "possible_keys": ["idx_group_id"],
          "key": "idx_group_id",
          "key_length": "3",
          "used_key_parts": ["group_id"],
          "ref": ["const"],
          "rows": 2,
          "filtered": 100
        }
      },
      {
        "block-nl-join": {
          "table": {
            "table_name": "p",
            "access_type": "ALL",
            "possible_keys": ["PRIMARY", "idx_group_id"],
            "rows": 7,
            "filtered": 100,
            "attached_condition": "p.group_id = 10 and p.product_id in (94,96,136,90,252,95,251,84,85,88,47,253,138,93,87,139,83,256,137,248,89,82)"
          },
          "buffer_type": "flat",
          "buffer_size": "1Kb",
          "join_type": "BNL"
        }
      }
    ]
  }
}