Since version 2.26. SNIP can add content from a block that was made with the new block editor (called Gutenberg). Here is how that works:

Here is a quick animated GIF upfront. It shows how to do it very quickly. Below you can find a step-by-step guide.

1. Edit one of your posts, pages or any custom post type.
2. Select a block containing content that you want to integrate into a schema.
3. In the top right, make sure that “Block” is selected.
4. In the right sidebar, scroll down until you see the “Advanced” box. Open it up!
5. Enter one or more CSS class names (separated by a white space). Remember one of it.
6. Update/Publish your post.
7. Then open up your Global Snippet / Schema Template and edit the property you want to add the content from the block.
8. In the text field that pops up, enter (only) one of the CSS class names.
9. Save your settings.