I don’t see the Yoast internal linking meta box
REST API Required
The Yoast internal linking meta box was introduced in Yoast SEO for WordPress Premium 4.0 and requires WordPress 4.7 or higher which includes native support for the REST API. You can check your current WordPress version by clicking on the WordPress logo in the top-left corner of your WordPress installation.
The link suggestions in the internal linking meta box are available for all languages.
Custom post types
Custom Post Types created by both plugins and themes are expected to be supported. After a short period of time, the link suggestions meta box is expected to show up when content is added. If the internal linking box fails to show up please contact support through the appropriate channel here.