Insert Gallery into Post Does Nothing

I created and published a lightbox gallery, but I cannot insert it in a post.
Here are the steps that I have taken:

In the post, I create the post block of the “lightbox gallery type”.
I go to to the gallery selector.
I select my gallery.
The button at bottom right (“Insert gallery into Post”) becomes active.
I click it, but nothing happens.
Nothing changes on the page current page.
I have to click “X” to get out.
I am on WP 5.6
Responsive Lightbox & Gallery 2.3.1
I was using Google Chrome.

Please help!
Otherwise, I can’t use Lightbox.

Jean Bertrand