How does “Animate on custom selector” work?

Yes, I understand the difference between animation panel and interaction layers.

But what I need is an explanation how to use the option “Animate on custom selector” in animation panel, because whatever I try, it has no effect.

https://gstest2.s2-tastewp.com/

1 animated container in the middle of the page (works without “Animate on custom selector” in animation panel.)

I added class .anitrig1 to intended trigger (below) and in animation panel in field “Custom selector”, but obviously with no working animation.

That’s the problem.

The “empty block” is not empty, but a regular box container with regular text within and with an added flip animation, which works regular, if I turn “Animate on custom selector” off. – Like I have done now with a copy of the block. (Look at it.)

But the question is, how can I use “Animate on custom selector”?

I understand what you say, but I don’t understand the plugin in this case.

“Animate on custom selector” is a regular option in regular animation panel without any hint by activation, that it needs special actions or additional features, only a input field for custom selector (which I can’t bring to work as expected).

To be open, I can live without this option, it is nor really essential for me. My primary interest is understanding this option (and many others), because I’m planning an intense WordPress workshop in the near future with Greenshift as a central tool. And I wanted to avoid telling my students “Oh, ignore this option, I don’t know how it works …”