You can try the "Verify integrifty of game files" option in Steam. You can find it by right clicking Divinity: Original Sin 2, opening the Properties window, and navigating to the "Local Files" tab. It should be at the very bottom. Note that this data comes from Divinity Original Sin 2 and not from the Divinity Engine 2 app in Steam.
If that does not work, I would recommend backing up your mod, removing the Divinity Engine 2 Data DLC from your DOS2 installation in steam, and then deleting the Editor, Public, Mods and Projects folders from your data folder.
To back up your mod(s), you will need to copy the following folders:
Data/Editor/Mods/{YourModName}
Data/Public/{YourModName}
Data/Mods/{YourModName}
Data/Projects/{YourModName}
Once your data folder is 100% clean, you can try re-installing the Divinity Engine 2 Data DLC in Steam, creating a new mod and building Story. If you are still unable to build Story at this point, your editor data may be corrupted by any mods you have installed (clear the "Documents\Larian Studios\Divinity Original Sin 2\Local Mods" and "Documents\Larian Studios\Divinity Original Sin 2\Mods" folders).
Once you are able to build in a clean project, you can move your mod files back to the data folder.
