did you change something inside vendor folder of Magento ?
If Yes, you should not change there, that directory is core directory and supposed to be not pushed to git, or files can be deleted from there when module upgrades etc.
You should extend files in
app/code - To create module/to edit module
app/design - To create theme/to edit theme
If you have already resolved, no need to share if working for you !
Yes i changed in file default C:\xampp\htdocs\magento3\vendor\magento\module-cms\view\frontend\layout
And than add a new block in backend
Current default file below:
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceContainer name="footer">
<container name="cms_footer_links_container" label="CMS Footer Links" htmlTag="div" htmlClass="links" before="footer_links" />
</referenceContainer>
<referenceBlock name="footer_links" remove="true">
<block class="Magento\Framework\View\Element\Html\Link\Current" name="privacy-policy-link">
<arguments>
<argument name="label" xsi:type="string" translate="true">Privacy and Cookie Policy</argument>
<argument name="path" xsi:type="string">privacy-policy-cookie-restriction-mode</argument>
</arguments>
</block>
</referenceBlock>
<referenceContainer name="footer-container">
<container name="footer" as="footer" label="Page Footer" htmlTag="div" htmlClass="footer content">
<block class="Magento\Cms\Block\Block" name="footer-custom-link" after="-">
<arguments>
<argument name="block_id" xsi:type="string">my_custom_footer</argument>
</arguments>
</block>
</container>
</referenceContainer>
</body>
</page>