Thirdy

Generates a simple RSS 2.0 rss.xml containing published posts with full post content. Admin UI to regenerate and shows file path/URL.
White-Label your WP RSS Feed
Two ways to install: 
1. Via WordPress Plugin Directory on your site 
2. Via https://wordpress.org/plugins/rsswire/
The Official Site is at https://thofficial.infree.page/index.php/rsswire/

RSSWire

Generates a simple RSS 2.0 rss.xml containing published posts with full post content. Admin UI to regenerate and shows file path/URL.

MailerLite

This plugin automatically adds featured images of your posts into the RSS feed.
Features:
<ul>
<li>Automatically adds featured images of your posts into the RSS feed</li>
<li>Choose from all available image sizes</li>
<li>Choose from multiple image alignment options</li>
</ul>

Featured Image in RSS Feed by MailerLite

This plugin automatically adds featured images of your posts into the RSS feed.

RSSWire vs Featured Image in RSS Feed by MailerLite