Ah, I didn’t notice you can’t close the teaser with Opt-in Panel.
My idea with the advanced floating plugin was to replicate the teaser, since it does have a close button, but this requires you to also have a separate opt-in plugin which supports opening the popup from a link.
I dug around a little more but I can’t find anything else quite like this available at the moment. As an alternative, you could hire a developer to make you a custom plugin at Envato Studio. All developers on there are vetted by Envato.
You may even be able to find someone willing to modify the Opt-in Panel plugin and add a close button.