Elements that are hidden (by clicking on the eye icon on track view) are not accessible because they are not visible on the canvas. It's really difficult to interact with, unless you know there's an invisible element somewhere on the canvas and you are able to select it.
This design propose using the boundary as an indicator for hidden elements.
When it's hovered (or selected), a visibility control button appears on the corner. Clicking on the button reveals the hidden content. Note that when the element becomes visible through this control button, it doesn't mean the element is set to visible as normal state. Therefore the button with red bar does not disappear when the element is out of focus (when user is interacting with other elements). The button then serves as an indicator: the element is still hidden even though you can see it.
We can further append more buttons to the preview button for showing different states. And, since we show the boundaries of hidden elements, the hidden elements should be selectable also on the canvas. Now it can only be done in track view.