Render block via twig template I have programmatically created a block. In my module folder I added all suggested templates in a templates folder(mymodule/templates/suggestedtemplatename.html.twig).

However the block is not using any of them!
I have enabled the theme debugger which gives me all the suggestions and describes which part of the page is produced from which template. I can see only block.html.twig producing html.
I tried drush cr and uninstalling/installing the module
I was missing the implementation of hook_theme. In order to use the template you need to declare it there.
FX

/**
 * Implements hook_theme().
*/
function mymodule_theme() {
  return array(
    'block__newsletter' =&gt; array(
      'render element' =&gt; 'elements',
    ),
  );
}


You should then have a templates/block--newsletter.html.twig.