Fish-Networking comes with a powerful scene manager tool that enables you to synchronize networked scenes with minimal effort, while also exposing a lot of powerful options.
General
The SceneManager Component has many scene features to support your multiplayer needs. The links below will take you to the different guides for each feature that the SceneManager has to offer.
Visit the API to see the public items exposed to the user in the SceneManager.
If you simply want an online scene to be loaded when the network starts and a different one to be loaded when it stops, then you can do that with a single component.
"Scene Caching" is the ability for the Server to keep a scene loaded when either all clients have unloaded that scene, or stopped observing that scene.
Fishnet has the ability for users to create their own Custom Scene Processor for loading and unloading scenes. Using Addressables for example, would need a Custom Scene Processor created.