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 (
    73433, 73432, 73431, 73430, 73429, 73428, 
    73427, 73426, 73425, 73424, 73423, 
    73422, 73421, 73420, 73419, 73418, 
    73417, 73416, 73415, 73414, 73413, 
    73412, 73411, 73410, 73409
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00051

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_products_categories range PRIMARY,pt pt 3 25 Using where; Using index
1 SIMPLE cscart_categories eq_ref PRIMARY,c_status,p_category_id PRIMARY 3 toolboxdigitalshop_dev.cscart_products_categories.category_id 1 Using where

Result

product_id category_ids
73409 1M
73410 1M
73411 1M
73412 1M
73413 1M
73414 1M
73415 1M
73416 1M
73417 1M
73418 1M
73419 1M
73420 1M
73421 1M
73422 1M
73423 1M
73424 1M
73425 1M
73426 1M
73427 1M
73428 1M
73429 1M
73430 1M
73431 1M
73432 1M
73433 1M