I was excited when I read about the on-demand button, similar to the on-screen keyboard on Windows 10, but its implementation is either broken and poorly described. I'm using a mouse, not a touch device.
With the toggle activated from Zorin Appearance > Screen Keyboard in Panel, the virtual keyboard activates itself whenever a text field is in focus. It was supposed to be passive until the button on the panel is pressed.
This was already accomplished via the Settings>Accessibility>Typing>Screen Keyboard toggle.
In reality, by activating it via the latter, you get almost a real on demand toggle as the Screen keyboard toggle is inside the sub-menu of the Accessibility tray icon. The catch is that at least one other option must be permanently activated otherwise the accessibility icon disappears.