Inline entity form complex and cardinatlity
Try changing the type to inline_entity_form_complex so that you have the following;

$form['inline_entity_form'] = [
    '#type' =&gt; 'inline_entity_form_complex',
    '#op' =&gt; 'add',
    '#entity_type' =&gt; 'my_ent_type',
    '#bundle' =&gt; 'my_bundle',
];


Got the pointer from the following answer. https://drupal.stackexchange.com/a/207582/9906