zen_mode

You can add this component to the winbar section of heirline opts.

require("heirline-components.all").component.zen_mode()

You can click the zen_mode button to toggle zen mode

As in this example

Be aware depending your heirline/zen_mode settings, you winbar might not be displayed during zen_mode. If that's your case you will have to run :ZenToggle when you want to exit.