Actually you can! In the bottom left of the camera there’s that diamond icon with the two lines under it? Show current drawing on top - that should isolate whatever you’re drawing with your art layers
That’s because it’s main function is to show the selected drawing on top of others. It’s an extra that it also isolates the selected art layer, if you turn Preview off. “Current Drawing On Top And Isolate Art Layer” would be a quite long name but Toon Boom does tend to have big descriptors on tools.