How do I include a twig file in a custom block type module?
Create a theme hook with the template name by replacing dashes with underscores:

mymodule.module:

/**
 * Implements hook_theme().
 */
function mymodule_theme() {
  return [
    'block__bundle__jumbotron' =&gt; [
      'render element' =&gt; 'elements',
      'base hook' =&gt; 'block',
    ],
  ];
}