Hello,

Actually, the Product Categories widget in the sidebar comes from WooCommerce end and there isn’t such a specific option available for that.

So, the best way possible in this regard is to choose the Category first from the Sidebar and then use the In Stock filter > then it will generate the correct URL in the address bar with the Category selected. Like the following URL from the Test Site: https://blackpearlspro.com/woodmart_support/product-category/computer-office/?stock_status=instock

This is the best way possible in this regard.

Best Regards.