Check if node update is published I've a content type with a workflow.
I have to notify users when the published version of the node is update.

Have I to check which transition is used? How?

I'm using an hook_node_presave.

[EDIT]
It seems that check if it's the default revision could be right:

 $entity-&gt;isDefaultRevision();


From draft to draft is false.
From draft to published is true.
From published to published is true.

Could be the right way?
As an alternative, consider using the Content moderation notifications module:


  Allows notifications to be sent to all users of a particular role, or to the content's author when a piece of content is transitioned from one state to another via core's content_moderation module.


I've used it with good results in several sites.