cannot use catch gallery

I have activated Catch Gallery. I should find Gallery under theme options now (in the Customizer) but it's not there. What can I do? www.riendummydomein.nl I tried the following, as you suggested in a previous question: Edit the page where you want to add the Catch Gallery. Now Add a new block => Formatting => Classic => Click on Add Media button => Create Gallery => Select the images you want in the gallery => Click on Create a new gallery => On the right side you will Gallery Settings select your option and Click on Insert Gallery. But when I add a new block and choose Classic Paragraph, I don't see the option Click on Add Media Button. This is where I get stuck... Thanks, Rien