Question about Plugin

I am aware from the description of the plugin that the shortcode can be used to display posts from a specific user:

[latestbyauthor author="username" show="3"]

However, how could I use a loop? Let’s say I am storing the author username in a variable since it will depend on which profile [of let’s say a student] is being shown (the posts by the student will show up on the specific student’s profile). For instance,

// get the author's username field of the student meta box cuz student is a custom post type and the metabox links the student post type to the author username
$the_username = get_post_meta($post->ID, 'gt_student_un', true)

Then I could do something like…

[latestbyauthor author="$the_username" show="3"]

https://wordpress.org/plugins/latest-posts-by-author/