Hi, this seems a little too easy, but I was just able to add a Youtube Channel, or at least a playlist within a channel, by simply pasting the url into a Squarespace video block. Here's what I did:
1. From the Youtube Channel, click "Play All" above your list of videos.
2. This creates a playlist in Youtube. Click Share and copy the playlist shareable URL.
3. Paste the URL into a Squarespace Video Block. Don't use Youtube's embed code, use the URL.
For me, this is working perfectly. But I haven't tested yet/don't know whether it automatically adds new videos to this playlist as they're posted. I'll post an update when I find out whether or not it automatically adds new videos (once my client adds a new video).
UPDATE 6/22/20: Ok, the solution I posted was really close but not quite because it continued to show the original most recent video in the playlist. You can see how this is written into the url: https://www.youtube.com/watch?v=Jha5eAMNTSg&list=UUwrA5BOmF6l_zA6QNeao11g
However, if you go to your Youtube dashboard, click on your playlist from the side panel, and click the share button, it creates a share link for the playlist only, and this updates to display the most recent video whenever you add it. Yay! You can see that this url doesn't designate a specific video: https://www.youtube.com/playlist?list=UUwrA5BOmF6l_zA6QNeao11g. Attaching a screenshot of what this looks like in your Youtube dashboard so you can get the right link.