Disable backorder on variation level

Hi,

I have problem with product variations stock.
I have the attibute “size” as variations loaded in to Woocommerce from my external shop system.

When the stock is set to 0 in the variation, it can still be selected because backorders are standard set as allowed per variation. I don’t work with backorders at all. I even set backorders not allowed on the product level (see: https://prntscr.com/ilts8i )

How can I solve this that backorders are not allowed for the variations? I have more than 10.000 products, I can’t change backorder option for all variations for all products.

Is there a way to disable backorders in general?

Thank you!

Kind regards,
Yorick