Is there a way to generate dummy content for custom entities?
To create some demo entities programmatically, you can use a while loop in your function.  To create 100 entities:

$i = 1;
while ($i &lt;= 100) {
  $i++;

  // Create an entity here.  See https://www.drupal.org/docs/8/api/entity-api/working-with-the-entity-api#s-create
  // To create random strings (e.g. for fake titles), refer to the comments at https://www.php.net/manual/en/function.rand.php -- In here you will find different ways to create random strings.
  // Generate some Lorem Ipsum text if you like: https://stackoverflow.com/a/20633400/861826

}