SELECT 
  cscart_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_products_categories.link_type = "M", 
      CONCAT(
        cscart_products_categories.category_id, 
        "M"
      ), 
      cscart_products_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  cscart_products_categories 
  INNER JOIN cscart_categories ON cscart_categories.category_id = cscart_products_categories.category_id 
  AND cscart_categories.storefront_id IN (0, 1) 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
  LEFT JOIN cscart_products_categories AS product_position_source ON cscart_products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 43213 
WHERE 
  cscart_products_categories.product_id IN (
    135, 136, 137, 138, 139, 140, 141, 142, 
    143
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00032

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.165243857,
    "nested_loop": [
      {
        "read_sorted_file": {
          "filesort": {
            "sort_key": "cscart_products_categories.product_id",
            "table": {
              "table_name": "cscart_products_categories",
              "access_type": "ALL",
              "possible_keys": ["PRIMARY", "pt"],
              "loops": 1,
              "rows": 138,
              "cost": 0.03161949,
              "filtered": 22.46376801,
              "attached_condition": "cscart_products_categories.product_id in (135,136,137,138,139,140,141,142,143)"
            }
          }
        }
      },
      {
        "table": {
          "table_name": "cscart_categories",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "c_status", "p_category_id"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["category_id"],
          "ref": ["cscart.cscart_products_categories.category_id"],
          "loops": 31,
          "rows": 1,
          "cost": 0.059948606,
          "filtered": 100,
          "attached_condition": "cscart_categories.storefront_id in (0,1) and (cscart_categories.usergroup_ids = '' or find_in_set(0,cscart_categories.usergroup_ids) or find_in_set(1,cscart_categories.usergroup_ids)) and cscart_categories.`status` in ('A','H')"
        }
      },
      {
        "table": {
          "table_name": "product_position_source",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "pt"],
          "key": "PRIMARY",
          "key_length": "6",
          "used_key_parts": ["category_id", "product_id"],
          "ref": ["const", "cscart.cscart_products_categories.product_id"],
          "loops": 31,
          "rows": 1,
          "cost": 0.053804606,
          "filtered": 100
        }
      }
    ]
  }
}