Where did stacked image gallery blocks go?

I am working on my digital art portfolio site.  One thing I do is transform photographs into abstract art.  I want to show both the before and after images.  I have found injecting "twentytwenty" code into the header is a solution.  Important to point out that the code is dependent on using Stacked Image Gallery Blocks.  I am able to inject the code and it does work (score!).  The problem is, I seem to only be able to find "image gallery blocks" as a type of content to add under blog pages.  Am I missing something?  If not, is there a way to insert stacked image gallery blocks on this page: https://www.dnbartwork.com/portfolio/reformation or is there an alternative solution/work-around?

If I can figure out how to access stacked image gallery blocks, I'd also love to know how to make them full-bleed!

Your suggestions are most welcome!