Hello,
At the moment, the Products Grid / Carousel widget does not have a built-in option to sort products by stock status (out of stock first).
Inside the Grid / Carousel widget, the available ordering methods are Date, ID, Author, Menu order, meta value. Unfortunately, stock status is not one of the supported order options.
If you want to control what appears in the carousel, you can also use the Data source option (for example: Best Sellers) to limit only out-of-stock products shown.
https://ibb.co/ZpvhtL16
In the widget settings, there is also an option to hide out-of-stock products, which ensures only available products are displayed in the carousel: https://ibb.co/W4pWrj96
Best Regards,