Create New Posts Loop Templates

I am a newbie… but learning stuff all the time so I tried what you are asking.

Make your new template.
Put it in the Templates folder of the plugin.

Then when you use the shortcode… where it says “Templates” put your template name in there.

You can test this by making a copy of the existing template, and name it something else and put it in the folder.
For example… make a copy of default-loop.php and name it default-looptest.php
And put default-looptest.php in the box where it says “Template” when you are using the shortcode “Posts” .