Most of my products avec a clean URL like : https://colecao-glorias.myshopify.com/products/documento-autografo-de-vinicius-de-moraes-1961
But some others (the one with a stock 0) have a not-friendly-for-seo URL "preview" like : https://colecao-glorias.myshopify.com/products_preview?preview_key=7f754b475d871d9287b6bcd6224c1733&...
I would assume the second url is for a product that is not published on the Online Storefront channel.
If you click the button/link to preview a product from within the Admin (and it is not published) it would create a url that looks like that.
Only you would see that url since only admins can preview unpublished products..