I’m sure @ zsviczian or others can provide more clarity, but here’s what I understand of it. While Excalidraw is a web app, it’s also a library that can be embedded in other applications. What this means for you is that when you run it as an Obsidian plugin, the core functionality is all running locally. There are still potential calls being made to external sources (e.g., if you want to install new libraries of images or new scripts to use with the excellent Automation Engine this plugin provides, those will require you to be online. But those should not be a concern in your normal day-to-day workflow. I use this on my iPad frequently and have not yet encountered any errors when I’m offline.