rss文件本身是xml，只要找到它的规范，使用php 数组转xml 就可以了

代码实现

$data=[
    'title'=>'写代码的崔哥',
    'link'=>'https://www.cuiwei.net/',
    'description'=>'一名PHP程序员，涉猎广泛：PHP，运维，前端，Android，iOS。会不定期给大家分享一些技术干货',
    'language'=>'zh-cn',
    'pubDate'=>gmdate ('l d F Y H:i:s', time()).' GMT',
    'lastBuildDate'=>gmdate ('l d F Y H:i:s', time()).' GMT',
    'docs'=>'https://www.rssboard.org/rss-specification',
    'generator'=>'cwf 1.0',
    'managingEditor'=>'chudaozhe@outlook.com (cw)',
    'webMaster'=>'chudaozhe@outlook.com (cw)',
];
$data['item']=[
    [
        'title' => 'aaa',
        'link' => 'https://www.cuiwei.net/p/1203489253',
        'description' => '描述。。。',
        'pubDate' => gmdate('l d F Y H:i:s', time()).' GMT',
        'guid' => '1203489253',
    ],
    [
        'title' => 'bbb',
        'link' => 'https://www.cuiwei.net/p/1126078311',
        'description' => '描述。。。',
        'pubDate' => gmdate('l d F Y H:i:s', time()).' GMT',
        'guid' => '1126078311',
    ],
];

$xml = new \SimpleXMLElement('<?xml version="1.0" encoding="utf-8"?><rss version="2.0"></rss>');
array_to_xml(['channel'=>$data], $xml);
echo $xml->asXML();

function array_to_xml($array, $xml=null){
    if (is_array($array)){
        foreach($array as $key=>$value){
            if(is_int($key)){
                if($key==0){
                    $node=$xml;
                }else{
                    $parent=$xml->xpath('..')[0];
                    $node=$parent->addChild($xml->getName());
                }
            }else{
                $node=$xml->addChild($key);
            }
            array_to_xml($value, $node);
        }
    }else{
        $xml[0]=$array;
    }
}

结果

<?xml version="1.0" encoding="utf-8"?>
<rss version="2.0">
    <channel>
        <title>写代码的崔哥</title>
        <link>https://www.cuiwei.net/</link>
        <description>一名PHP程序员，涉猎广泛：PHP，运维，前端，Android，iOS。会不定期给大家分享一些技术干货</description>
        <language>zh-cn</language>
        <pubDate>Sunday 03 April 2022 07:50:50 GMT</pubDate>
        <lastBuildDate>Sunday 03 April 2022 07:50:50 GMT</lastBuildDate>
        <docs>https://www.rssboard.org/rss-specification</docs>
        <generator>cwf 1.0</generator>
        <managingEditor>chudaozhe@outlook.com (cw)</managingEditor>
        <webMaster>chudaozhe@outlook.com (cw)</webMaster>
        <item>
            <title>aaa</title>
            <link>https://www.cuiwei.net/p/1203489253</link>
            <description>描述。。。</description>
            <pubDate>Sunday 03 April 2022 07:50:50 GMT</pubDate>
            <guid>1203489253</guid>
        </item>
        <item>
            <title>bbb</title>
            <link>https://www.cuiwei.net/p/1126078311</link>
            <description>描述。。。</description>
            <pubDate>Sunday 03 April 2022 07:50:50 GMT</pubDate>
            <guid>1126078311</guid>
        </item>
    </channel>
</rss>

参考

https://www.rssboard.org/rss-specification

https://www.php.net/manual/zh/book.simplexml.php