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 (
    66199, 66198, 66197, 66196, 66195, 66194, 
    66193, 66192, 66191, 66190, 66189, 
    66188, 66187, 66186, 66185, 66184, 
    66183, 66182, 66019, 66018
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00050

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_products_categories range PRIMARY,pt pt 3 21 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
66018 22M
66019 23,13M
66182 4M
66183 4M
66184 4M
66185 4M
66186 4M
66187 4M
66188 4M
66189 4M
66190 4M
66191 4M
66192 4M
66193 4M
66194 4M
66195 4M
66196 4M
66197 4M
66198 4M
66199 4M