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 = 6 
WHERE 
  cscart_products_categories.product_id IN (
    93938, 92908, 92679, 93934, 93931, 93930, 
    93929, 93927, 93907, 93906, 93905, 
    93902, 93796, 93784, 93544, 93459, 
    93069, 93068, 93797, 93774
  ) 
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
92679 6M 0
92908 6M 0
93068 6M 0
93069 6M 0
93459 6M 0
93544 6M 0
93774 6M 0
93784 6M 0
93796 6M 0
93797 6M 0
93902 6M 0
93905 6M 0
93906 6M 0
93907 6M 0
93927 6M 0
93929 6M 0
93930 6M 0
93931 6M 0
93934 6M 0
93938 6M 0