The game loads local files, so you don't have to publish your own mods when testing.
Publish local puts the packaged mod in Documents/Larian Studios/Divinity Original Sin 2/Local Mods for people who want to upload the mod to Nexus/etc. instead of Steam.
@Barbarossa it looks like you made a Adventure, instead of an Add-on? For extra levels, you'll want to make an add-on. Here's some
information on the difference between both modes. And here's some information on how you can see/enable
Adventures or
Add-ons. For adventures specifically, remember to press Generate Definitions and Build in the
Story Editor.