If menu link content entities are in the menu then they should also be in the cache tags

This might not actually be an issue because \Drupal\menu_link_content\Entity\MenuLinkContent::postSave() will result in clearing the cache tags of the affect menus.

See \Drupal\Core\Menu\MenuTreeStorage::save()

    $cache_tags = Cache::buildTags('config:system.menu', $affected_menus, '.');
    $this->cacheTagsInvalidator->invalidateTags($cache_tags);

Going to close this one because adding the cache tags for each entity feels like noise.