Getting the "Open link in a new tab" property from a WordPress menu item
Solution 1:
The below works in Timber v1.19.1 Twig v1.42.5
{% for item in menu.items %}
<li>
<a href="{{ item.link }}"
target="{{ item.meta( '_menu_item_target' ) ? item.meta( '_menu_item_target' ) : '_self' }}">
{{ item.title }}
</a>
</li>
{% endfor %}