<referenceContainer name="top.links">
           <block class="MagentoFrameworkViewElementHtmlLinkCurrent" name="collection">
                <arguments>
                    <argument name="label" xsi:type="string">collection</argument>
                    <argument name="path" xsi:type="string">collection</argument>
                </arguments>
          </block>
       </referenceContainer>

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="MagentoThemeBlockHtmlTopmenu">
        <plugin name="add_cms_menu" type="{VendorName}{ModuleName}PluginTopmenu" sortOrder="1" />
    </type>
</config>

appcode{VendorName}{ModuleName}PluginTopmenu.php



<?php
namespace {VendorName}{ModuleName}Plugin;
use MagentoFrameworkDataTreeNodeFactory;
class Topmenu
{
    protected $nodeFactory;
    protected $_storeManager;
    protected $_pageFactory;
    protected $_urlBuilder;

    public function __construct(
        NodeFactory $nodeFactory,
        MagentoCmsModelPageFactory $pageFactory,
        MagentoStoreModelStoreManagerInterface $storeManager,
        MagentoFrameworkUrlInterface $urlBuilder
    ) {
        $this->nodeFactory = $nodeFactory;
        $this->_pageFactory = $pageFactory;
        $this->_storeManager = $storeManager;
        $this->_urlBuilder = $urlBuilder;
    }
    public function beforeGetHtml(
        MagentoThemeBlockHtmlTopmenu $subject,
        $outermostClass = '',
        $childrenWrapClass = '',
        $limit = 0
    ) {
        /* Showing  Cms page About us at menu */
        $page = $this->getCmspage('about-us');
        if($page == null){
            return;
        }


        $node = $this->nodeFactory->create(
            [
                'data' => [
                    'name' => $page->getTitle(),
                    'id' => $page->getIdentifier(),
                    'url' =>  $this->_urlBuilder->getUrl(null, ['_direct' => $page->getIdentifier()]),
                    'has_active' => false,
                    'is_active' => false // (expression to determine if menu item is selected or not)
                ],
                'idField' => 'id',
                'tree' => $subject->getMenu()->getTree()
            ]
        );
        $subject->getMenu()->addChild($node);
    }
    protected function getCmspage($identifier){

        $page = $this->_pageFactory->create();
        $pageId = $page->checkIdentifier($identifier, $this->_storeManager->getStore()->getId());

        if (!$pageId) {
            return null;
        }
        $page->setStoreId($this->_storeManager->getStore()->getId());
        if (!$page->load($pageId)) {
            return null;
        }

        if (!$page->getId()) {
            return null;
        }

        return $page;
    }