Youtube limit number of posts returned for a specific query to 500. Fortunately we can still grab all videos from a channel using a little trick that WordPress Automatic supports

The idea is to return items sorted by date so we get newest items first (500 latest items) then once reached the 500 limit, we set the plugin to return items published before the date of the last video posted, so we get another 500 and so on

so just set the sorting to be by date

Then set the date of the last item found after the plugin stops adding new videos. i.e once reached the 500 limit