This creates a local copy (often an .f3d or .fusion archive file). This does not sync to your cloud account. When you reconnect to the internet later, you will need to manually upload this file to your project to merge it back into your cloud workflow.
Working in Fusion 360 offline is a critical skill for maintaining productivity during travel or internet outages. While it is primarily a cloud-based tool, you can leverage its and local caching to continue designing without a connection. How to Enable Offline Mode fusion360 offline