It's not really officially advertised but it is first party, this guide [0] shows how to find it but it's just https://www.youtube.com/feeds/videos.xml?channel_id=CHANNELI... and the guide just explains how to find CHANNELID since it isn't explicitly shared (which amounts to going a channel page, viewing page source, and searching for "browse_id" which will be a key in a JSON string where the value is the channel ID).