The data in the Vizarr viewer is only accessible to people that are signed in to the Fractal server. Otherwise, you can get an error like this: I get an Error: server replied with "Node not found: v3 array or group" when loading the resource
Go to one of your dataset and click “View image”

Explore example datasets: I want to see an example dataset
Look at your own dataset by changing the URL according to instructions here: What's the structure of the paths in the URL?
More direct ways of opening the vizarr viewer directly from Fractal web will be coming soon.