Hi,

When we manufacture, stock quantity is updated automatically; however, if you'd like to update it using code, use the following code.

self.env['stock.quant'].with_context(inventory_mode=True).create({
            'product_id': self.product.id,
            'inventory_quantity': 2.0,
            'location_id': self.stock_location_14.id
        }).action_apply_inventory()

Regards