//Files
/modules/ts_events/
/modules/ts_events/templates/block--ts-events.html.twig
/modules/ts_events/ts_events.info.yml
/modules/ts_events/ts_events.module //<-- code.
/modules/ts_events/config //<-- files to create custom block

//Code

<?php
function ts_events_theme() {
  $theme['block__ts_events'] = [
    'template' => 'block--ts-events',
  ];

	return $theme;
}

function ts_events_theme_suggestions_block_alter(array &$suggestions, array $variables) {
  $content = $variables['elements']['content'];
  if (isset($content['#block_content']) && $content['#block_content'] instanceof \Drupal\block_content\BlockContentInterface) {
    $suggestion = 'block__' . $content['#block_content']->bundle();
    array_splice( $suggestions, 1, 0, $suggestion );
  }
}