Drupal - Create a route to show a node with a custom display/view mode

In Drupal 8 there are two display modes: view mode and form mode.

You can define the view mode in a route using the _entity_view key.

_entity_view: The value is entity_type.view_mode. Will find an entity in the path and render it in the given view mode. E.g. _entity_view: node.teaser will return the render array of the {node} in teaser mode.