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 (
    101603, 101602, 101601, 101599, 101598, 
    101596, 101595, 101594, 101593, 101592, 
    101591, 101590, 101585, 101583, 101582, 
    101544, 102132, 102131, 102130, 102129
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00054

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_products_categories range PRIMARY,pt pt 3 20 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
101544 4M 0
101582 4M 0
101583 4M 0
101585 4M 0
101590 4M 0
101591 4M 0
101592 4M 0
101593 4M 0
101594 4M 0
101595 4M 0
101596 4M 0
101598 4M 0
101599 4M 0
101601 4M 0
101602 4M 0
101603 4M 0
102129 4M 0
102130 4M 0
102131 4M 0
102132 4M 0