Andreas (82MHz) shared this great tip in Mastodon. You can use yt-dlp and sed to get the RSS feed URL from Youtube channel URL.
#!/bin/bash
yt-dlp --playlist-items 0 -O playlist:channel_url --print channel_url $1 | sed 's|channel/|feeds/videos.xml?channel_id=|'Youtube also exposes the URL as rel="alternate" on the channel pages so if you’re just looking to add a channel to your RSS reader, you can use the channel URL as-is but this can be handy for other things, like manually managing some feeds for other use cases.