Front end forms is designed to create and edit a post and change its status , Also you cannot save a post revision without actually having the post in the database at least as Draft.
However you can use the Front End Forms API to create a revision of the post whenever it is edited through front end forms
for this purpose you can use the hook cred_submit_complete along with the WordPress function wp_save_post_revision
The code would be like
add_action('cred_submit_complete', 'my_success_action',10,2);
function my_success_action($post_id, $form_data)
{
// Run the code only for specific form
if ($form_data['id']==12)
{
// Save the post revision
//https://developer.wordpress.org/reference/functions/wp_save_post_revision/
wp_save_post_revision($post_id);
}
}
