I’ve tried out this plugin, and it’s easy to create blocks for those of us who don’t know much javascript, but are able to use PHP.

While creating a block uses only fields, the block developer is supposed to create a template to display the fields in both the front and backend. So it does become WYSIWYG, at least the way I did it, it was. The fields are simply the controls that most blocks have in the sidebar, but they appear in the editor content when you click to edit the block.

I’ve also used ACF, but this just seems lighter to me, if I need to create a custom block for a client.