Partly. Running templates and golden tests on DuckDB with files already on your machine works without a network connection. Writing code needs the model provider, so it needs a connection. Connecting, sampling and deploying need your platform, and publishing a dashboard needs Emolysis's services.
Signing in the first time needs a connection too, because every use of Emolysis needs an Emolysis account. After that, the app checks your plan when it is online, and your plan stays active through short periods offline.
In short: testing on local files works on a plane; writing code, deploying and sharing do not. See what leaves your machine and the data handling docs.