You can either:

1. Get the list of playlists for a channel from the Google API
2. Get it from the playlist URL, or convert directly from a ChannelID to one of its feeds.

Get your API key from Google Cloud API, choose Credentials and show an API key. (I chose Browser Key 3.)

export YTKEY=[YOURAPIKEY]

Get ChannelId from the channel's main page:

1. Navigate to the channel's page: Ex., https://www.youtube.com/@CartoonHangover
2. Click on “More…” or “About”
3. Click on “Share Channel” → “Copy Channel ID”

Then you can use the YouTube v3 API to retrieve playlists for that channel.

curl "https://www.googleapis.com/youtube/v3/playlists?part=snippet&channelId=UCIA9jUDnKVMYc4SmqTxcwqg&maxResults=50&key=$YTKEY"

This resulted in:

{
  "kind": "youtube#playlistListResponse",
  "etag": "Z2DN9FRRZRRZIWx2HM8EsNieJoE",
  "pageInfo": {
    "totalResults": 38,
    "resultsPerPage": 50
  },
  "items": [
    {
      "kind": "youtube#playlist",
      "etag": "2hc5G5VuRmc6R1CeDQnc9C0UNSY",
      "id": "PL2DcNkn8HAwR_7sj9S_shla9Wc521w6YW",
      "snippet": {
        "publishedAt": "2013-10-21T16:37:48.416149Z",
        "channelId": "UCIA9jUDnKVMYc4SmqTxcwqg",
        "title": "Latest Bravest Warriors",

Find your playlist, and get the feed. This one worked (but not always, sometimes a 404, maybe because rate limited):

https://www.youtube.com/feeds/videos.xml?playlist_id=PL2DcNkn8HAwR_7sj9S_shla9Wc521w6YW

Otherwise, if a channel has one main upload feed, you can follow these instructions to make a playlist feed directly from a channel ID.

I'm still getting 404s for these two feeds. :/

This is My public Favorites feed, so you'd hope this would work: https://www.youtube.com/feeds/videos.xml?playlist_id=FLEggwBSd9sM3nG3drXQjFhQ.

Channel ID for Extra History: UCCODtTcd5M1JavPCOr_Uydg. So presumably replace UC with UULF to convert the Channel ID to one of its playlists, this would work https://www.youtube.com/feeds/videos.xml?playlist_id=UULFCODtTcd5M1JavPCOr_Uydg

Also, API gave:

    {
      "kind": "youtube#playlist",
      "etag": "3i7uh4VFKeulC4sorjGgR63D4Ho",
      "id": "PLhyKYa0YJ_5BVvwMI_412K7PKndtzHTBa",
      "snippet": {
        "publishedAt": "2024-05-16T20:26:10.943743Z",
        "channelId": "UCCODtTcd5M1JavPCOr_Uydg",
        "title": "Extra History Complete",
        "description": "#History #Documentary #Explained #Education #WorldHistory",

So you'd hope https://www.youtube.com/feeds/videos.xml?playlist_id=PLhyKYa0YJ_5BVvwMI_412K7PKndtzHTBa would be valid.