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 (
    35929, 35931, 35930, 35925, 35923, 32703, 
    32706, 32704, 35917, 35916, 32678, 
    33081, 35928, 35927, 35921, 32679, 
    32687, 32681, 32683, 32696, 32685, 
    32707, 32691, 35912, 32690, 35919, 
    35920, 32695, 32700, 33102
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00693

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products_categories",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "pt"],
          "key": "pt",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "rows": 30,
          "filtered": 100,
          "index_condition": "cscart_products_categories.product_id in (35929,35931,35930,35925,35923,32703,32706,32704,35917,35916,32678,33081,35928,35927,35921,32679,32687,32681,32683,32696,32685,32707,32691,35912,32690,35919,35920,32695,32700,33102)"
        }
      },
      {
        "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": ["dev_db.cscart_products_categories.category_id"],
          "rows": 1,
          "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')"
        }
      }
    ]
  }
}