I installed ArcGIS Enterprise, Portal and server works fine but when I tried to access items from portal folder I receive a warning saying to sign in to access the item. Did I miss some config?
it looks like you're using a hostname in the 'web map':
you would typically using a fully-qualified domain name there:
the fully qualified domain name is typically trusted whereas the hostname is not. Have you got an alias to use? That's a particularly gruesome URL otherwise. I strongly recommend create an alias before you start loading any content. e.g. mygis.domain.com.
Just to add to Scott's answer, if this is a new Enterprise and you've registered the web adaptor for Portal and Server - you may need to amend the web adaptors to use a friendly DNS alias on the registration page. Please see: