How do I get the submitted moderation state of a custom block?
all most there try the following 

// Get the current  entity.
$entity = $form_state-&gt;getFormObject()-&gt;getEntity();
$moderation_state = $entity-&gt;get('moderation_state')-&gt;getString();
// Do the things.


or 
   in a submit or validation thing 
   try to 

// use dump() as it is way better 
dump($form_state-&gt;getValues()) // &lt;-- and find in the array