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 (
    96060, 95699, 95231, 93055, 89231, 96061, 
    95337, 92918, 96004, 96003, 96002, 
    95999, 95972, 95837, 95802, 95740, 
    95700, 95697, 95062, 95040
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00050

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
89231 6M 0
92918 6M 0
93055 6M 0
95040 29,6M 0
95062 6M 0
95231 29,6M 0
95337 6M 0
95697 6M 0
95699 6M 0
95700 6M 0
95740 6M 0
95802 6M 0
95837 6M 0
95972 6M 0
95999 6M 0
96002 6M 0
96003 6M 0
96004 6M 0
96060 6M 0
96061 6M 0