Good morning!  I am looking for a dairy free frosting that I can use under fondant.  I've made a version of ABC with shortening  in the past, but found it didn't firm up quite as much as I like, when I'm working with fondant. I typically use SMBC when I'm working with fondant, and am worried that using shortening in it instead of butter still won't firm up well.  Thoughts? Suggestions? Recipes?  Thanks!

https://www.gretchensbakery.com/aquafaba-swiss-buttercream-recipe/

Using shortening in place of butter in my SMBC has worked well for me even under fondant. Some SMBC recipes have been modified to add a little powdered sugar at the end. I find that will help firm things up in a pinch.