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 = 1 
WHERE 
  cscart_products_categories.product_id IN (
    86818, 86816, 86673, 86546, 86298, 86564, 
    87403, 87401, 86580, 88424, 86807, 
    86875, 86874, 86872, 86869, 86867, 
    86866, 86771, 86770, 86769
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00056

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_products_categories range PRIMARY,pt pt 3 22 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
86298 1M 0
86546 1M 0
86564 1M 0
86580 28,1M 0
86673 1M 0
86769 1M 0
86770 1M 0
86771 1M 0
86807 28,1M 0
86816 1M 0
86818 1M 0
86866 1M 0
86867 1M 0
86869 1M 0
86872 1M 0
86874 1M 0
86875 1M 0
87401 1M 0
87403 1M 0
88424 1M 0