In Magento 2, main quantity which you see in the qty field of the product might be different than salable quantity. Customers can buy buy products according to salable quantity only. Salable quantity is calculated using main quantity in product and entries available in inventory_reservation table for that product.
Logic of salable quantity for any sku is:
You can Add new group from:
Stores -> Attributes -> Attribute Set
Click on Your attribute set
In the Groups Click Add New . It will create a New Group.
If you want to put it below Content Group, You can drag it using mouse.
In the Screen Shot, I created a Test Group
Unfortunately, more information would be needed to get to the bottom of this problem. I should ask this: I am not clear on whether or not this issue happens on the product edit page or an attribute's edit page?
Set a breakpoint at the first line of pub/index.php (or index.php if that is the entry point). Evaluate the incoming $_POST vars.
Set a ...
I don't believe this is currently possible to achieve through configuration in Magento 2.3, see this github issue for reference. It is possible to allow all countries for shipping and restrict the payment methods based on country, but not vice versa. A Magento extension would have to be implemented (or purchased) to achieve this behaviour. I am unsure of any ...