add Bundle field to a custom entity
For the Entity base field update, You'll need to also add an update hook to apply it
For example:
Installing a new field storage definition
use Drupal\Core\Field\BaseFieldDefinition;

/**
 * Implements hook_update_N
 */
function example_update_8701() {
  $bundle = 'article';
  $field_storage_definition = BaseFieldDefinition::create('text_long')
  -&gt;setLabel(t('New Name'))
  -&gt;setDisplayOptions('form', [
    'type' =&gt; 'text_textarea',
  ])-&gt;setRevisionable(TRUE)
  -&gt;setTargetBundle($bundle);

  \Drupal::entityDefinitionUpdateManager()
    -&gt;installFieldStorageDefinition('new_name', 'node', 'EXAMPLE_MODULE', $field_storage_definition);
}

Documentation: https://www.drupal.org/node/3034742