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 = 88 
WHERE 
  cscart_products_categories.product_id IN (
    125139, 125138, 125136, 125123, 125652, 
    125492, 125025, 125024, 125020, 125568, 
    125566, 124982, 125496, 124870, 124859, 
    124858, 125412, 125411, 124963, 124733, 
    124731, 124573, 124546, 124358, 124737, 
    124650, 124299, 124231, 124217, 124215
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00086

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_products_categories range PRIMARY,pt pt 3 68 Using where; Using index
1 SIMPLE product_position_source eq_ref PRIMARY,pt PRIMARY 6 const,toolboxdigitalshop_dev.cscart_products_categories.product_id 1
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 position
124215 29,88,4M 0
124217 88,4M 0
124231 88,4M 0
124299 88,4M 0
124358 88,4M 0
124546 29,88,4M 0
124573 88,4M 0
124650 88,4M 0
124731 29,88,4M 0
124733 88,4M 0
124737 88,4M 0
124858 88,4M 0
124859 21,88,4M 0
124870 29,88,4M 0
124963 88,4M 0
124982 88,4M 0
125020 29,88,4M 0
125024 29,88,4M 0
125025 88,4M 0
125123 88,4M 0
125136 29,88,4M 0
125138 88,4M 0
125139 88,4M 0
125411 88,4M 0
125412 88,4M 0
125492 88,4M 0
125496 88,4M 0
125566 88,4M 0
125568 88,4M 0
125652 88,4M 0