How to subscribe to YouTube channels via RSS.
YouTube – Take the name of the channel in this case:
https://www.youtube.com/channel/UCvavJlMjlTd4wLwi9yKCtew
Change the text in red above to the text in green below. The channel ID string is the same as is the primary url for youtube.com
https://www.youtube.com/feeds/videos.xml?channel_id=UCvavJlMjlTd4wLwi9yKCtew