The Block Editor / Gutenberg and Elementor are not the same, although they're both for building pages. With page builders such as Elementor, you can only choose to build your page using Elementor, or the WordPress Block Editor.
You can have some pages built using Elementor, and some pages built using the Block Editor. You cannot use both at the same time for the same page.
While Stackable is compatible with Elementor, this means that you can have both of the plugins activated at the same time on your site. You cannot use Stackable blocks (or any WordPress blocks) within the editor of your page builder.