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 = 4 
WHERE 
  cscart_products_categories.product_id IN (
    88704, 88703, 88702, 88701, 88700, 88699, 
    88698, 88696, 88695, 88694, 88692, 
    88691, 88690, 88688, 88687, 88686, 
    88685, 88684, 89281, 102419
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00072

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_products_categories range PRIMARY,pt pt 3 23 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
1 SIMPLE product_position_source eq_ref PRIMARY,pt PRIMARY 6 const,toolboxdigitalshop_dev.cscart_products_categories.product_id 1

Result

product_id category_ids position
88684 4M 0
88685 4M 0
88686 4M 0
88687 4M 0
88688 29,4M 0
88690 4M 0
88691 4M 0
88692 4M 0
88694 29,4M 0
88695 4M 0
88696 4M 0
88698 4M 0
88699 4M 0
88700 4M 0
88701 4M 0
88702 4M 0
88703 4M 0
88704 4M 0
89281 29,4M 0
102419 4M 0