Hello,
Sorry to hear about the inconvenience.
We have confirmed this issue from the Test Site with the updated WoodMart Theme, Core plugin and WooCommerce version. The Quantity input under the Header Mini Cart is working fine.
Can you please once try deactivating all the 3rd party plugins and activate only theme-required plugins on the site and then check the issue. We are sure your issue will be solved. Then Activate the 3rd party plugins one by one and check which plugin is creating the issue for you.
If the issue still persists, then please remain 3rd party plugins deactivated and share the valid WP-ADMIN Login details of your Site in the below listed format on which you are facing the issue so that we can look after the mentioned issue on your Site and assist you accordingly.
WP-ADMIN URL:
WP-ADMIN USERNAME:
WP-ADMIN PASSWORD:
Best Regards.