How can I programmatically render a node's field respecting the view mode settings?
To render a single field with the display setting of a view mode you can use the view() method of the field:

Example for rendering the image in teaser format:

$build['image'] = $node-&gt;field_image-&gt;view('teaser');


Or the body in full:

$build['body'] = $node-&gt;body-&gt;view('full');