I am not sure that i understand what you mean by parent level stock managment .
If you meant this managed stock is unticked anyway for all variant products : https://prnt.sc/10b7ev8
I manage my stock from variation tab on each product (>stock quantity option): https://prnt.sc/10b7m4o
I am also show you my settings in woocomerce>settings>inventory tab : https://prnt.sc/10b7trx
The problem remains,so to give you an example of the problem,and be more specific check this photo: https://prnt.sc/10b7olo
In this example i have use “filter by size” and i am searching for size 38 .You can see that a lot of products shown there ,aren’t available for this size.