Using Excerpts & Thumbnails with Templates

NOTE: Excerpts & Thumbnails is being discontinued. A new Templates add-on will be introduced very soon. Existing users of Excerpts & Thumbnails are urged to switch to this new add-on for displaying feed items. Learn more.

As of WP RSS Aggregator Core version 4.13, we introduced templates. This is the new rendering system for the plugin that replaces the old one also used by Excerpts & Thumbnails. Since these two work so differently to each other, here's a quick look at how the two work together right now.

Excerpts & Thumbnails can continued to be used with the [wp-rss-aggregator] shortcode the same exact way it was before Core v4.13. The same previous parameters apply.
If a shortcode is applied anywhere across your site includes the new "template" parameter, it switches that display to use the new rendering system, so it will no longer be compatible with the Excerpts & Thumbnails add-on.
The new Gutenberg block called "WP RSS Aggregator Feeds" introduced into Core v4.13 can not be used to display feed items with excerpts and thumbnails (using the Excerpts & Thumbnails add-on). The block only displays feed items using the new templates (found in RSS Aggregator > Templates).