Get meta tags programmatically

To access the meta tags field data created by the Metatag module you can use the Metatag Manager service.

$metatag_manager = \Drupal::service('metatag.manager');

First, get the tags from the entity (usually from a node):

$tags = $metatag_manager->tagsFromEntityWithDefaults($node);

and then generate the meta tag values:

$metatags = $metatag_manager->generateTokenValues($tags, $node);