Find your YouTube channel id by visiting your channel and looking in the address bar.
Add a direct link to the channel's feed:
https://www.youtube.com/feeds/videos.xml?channel_id=[YOUR_CHANNEL_ID]Note: Replace "[YOUR_CHANNEL_ID]" with the channel ID number that you found in step 1. For example, using the image above, that direct link would be https://www.youtube.com/feeds/videos.xml?channel_id=UCf9owOtSrhmE098diQabZgg.
Go to the RSS tab in the publisher and add a new RSS feed. Add the link you just created in step 2 into the 'RSS Feed URL' field.
Note: This also works with Playlists. Just use this format: https://www.youtube.com/feeds/videos.xml?playlist_id=[YOUR_PLAYLIST_ID].