Magento 2.3.5: system.xml file upload allow types not working

system.xml

<field id="upload_image_id" translate="label comment" type="image" sortOrder="50" showInDefault="1" showInWebsite="1" showInStore="1">
   <label>Select Image</label>
   <backend_model>NameSpaceYourModuleModelConfigBackendImage</backend_model>
   <base_url type="media" scope_info="1">yourfolder</base_url>
</field>

Image.php

namespace NameSpaceYourModuleModelConfigBackend;

class Image extends MagentoConfigModelConfigBackendImage
{
/**
 * The tail part of directory path for uploading
 *
 */
const UPLOAD_DIR = 'yourfolder'; // Folder save image

/**
 * Return path to directory for upload file
 *
 * @return string
 * @throw MagentoFrameworkExceptionLocalizedException
 */
protected function _getUploadDir()
{
    return $this->_mediaDirectory->getAbsolutePath($this->_appendScopeInfo(self::UPLOAD_DIR));
}

/**
 * Makes a decision about whether to add info about the scope.
 *
 * @return boolean
 */
protected function _addWhetherScopeInfo()
{
    return true;
}

/**
 * Getter for allowed extensions of uploaded files.
 *
 * @return string[]
 */
protected function _getAllowedExtensions()
{
    return ['jpg', 'jpeg', 'gif', 'png', 'svg'];
}

Still not allowing it I get Disallowed file type. Anything else missing ?