Can I reference field item & label in node.html.twig?
If you can't find the label somewhere inside of content, then the code, which will prepare the label for rendering did not run at this point.

If you are inside the node twig, then there is a fully loaded node object. You can use this to get the field definition and the label:

{{ node.field_myfield.fieldDefinition.label }}


Or the first field item:

{{ node.field_myfield.0.value }}