How do I remove default category in WordPress automatically?

Hello,

Thanks for the feedback!

If you need to remove/set new terms during a Post Action in the ACF Extended Form module, you should use the acfe/form/submit/post hook. See documentation. This hook will let you perform an action right after a post creation/update. Usage example:

add_action('acfe/form/submit/post/form=my-form', 'my_form_submit', 10, 5);
function my_form_submit($post_id, $type, $args, $form, $action){
    
    wp_remove_object_terms($post_id, 'uncategorized', 'category');
    
}

Hope it helps!

Have a nice day!

Regards.