To toggle line visibility on and off, you can make use of the 'ButtonDownFcn' callback of the legend instead. Please see the below link for more information on this callback:
I have attached a sample app that demonstrates how to do this. In summary, the app does the following:
1. It has a UIAxes, and at startup it plots lines and a legend onto this UIAxes
2. It then sets the legend 'ButtonDownFcn' callback to be a custom function that is part of the App itself
3. In this custom function, we use the 'Event data' argument to determine where in the legend was clicked
4. Once we have where was clicked, we can use that to roughly map back to what line number in the legend that corresponds to.
5. We can get all the lines from 'app.UIAxes.Children', and then choose the appropriate line with the line number we got in the previous step.
6. Then, we can toggle the 'Visibility' property of that line to 'off' or 'on' accordingly