I can’t find the place to switch the Avia layout builder to HTML source code.
You can click “Editeur par defaut” at the top to switch to default editor. If you would like to get the shortcodes of ALB elements, please refer to this post – https://kriesi.at/documentation/enfold/intro-to-layout-builder/#debug-mode and enable debugging mode. Shortcodes should appear right below Advanced Layout Builder.
If that is not what you meant, please elaborate :)