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 
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') 
WHERE 
  cscart_products_categories.product_id IN (
    347, 346, 345, 344, 343, 342, 341, 340, 
    339, 338, 335, 334, 333, 332, 331, 330, 
    325, 324, 323, 322, 321, 320, 319, 318, 
    317, 316, 315, 314, 313, 312, 311, 310, 
    309, 308, 307, 306, 305, 304, 303, 302, 
    301, 300, 299, 298, 297, 296, 295, 294, 
    293, 292, 291
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00083

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_products_categories.product_id",
      "temporary_table": {
        "nested_loop": [
          {
            "table": {
              "table_name": "cscart_categories",
              "access_type": "ALL",
              "possible_keys": ["PRIMARY", "c_status", "p_category_id"],
              "rows": 11,
              "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": "cscart_products_categories",
              "access_type": "ref",
              "possible_keys": ["PRIMARY", "pt"],
              "key": "PRIMARY",
              "key_length": "3",
              "used_key_parts": ["category_id"],
              "ref": ["v8.cscart_categories.category_id"],
              "rows": 1,
              "filtered": 98.11320496,
              "index_condition": "cscart_products_categories.product_id in (347,346,345,344,343,342,341,340,339,338,335,334,333,332,331,330,325,324,323,322,321,320,319,318,317,316,315,314,313,312,311,310,309,308,307,306,305,304,303,302,301,300,299,298,297,296,295,294,293,292,291)"
            }
          }
        ]
      }
    }
  }
}