There are at least two methods to get this done. Here's the method I used and below is the outline of a method I found in the book Mastering Drupal 8.
This is a simple overriding process. Get a copy of the page.html.twig from the Bootstrap parent theme folder and copy it into our subtheme/templates directory.
First, we need to create a jumbotron region. This can be accomplished by modifying the page.html.twig file with the following snippet.
Above the #Main section, we'll paste this block. Use your own image
{# Jumbotron #}
{% if page.jumbotron %}
{% block jumbotron %}
<div class="container">
<div id="jumbotron" class="jumbotron">
<img src="/sites/default/files/2018-06/womens_center.jpg" class="img-responsive">
{{ page.jumbotron }}
</div>
</div>
{% endblock %}
{% endif %}
Then we clear the cache and go back to the Blocks UI. We will then place a jumbotron block in the Jumbotron region.
The second method to accomplish this is:
Create a custom block, add fields to hold the text or a button
Add the new block
Modify the tnode emplate per naming convention for node--page--full.html.twig
I haven't tried this second method, but it is more complete and perhaps a more proper approach.