sysbird

This block fetches only the most recent item from another site’s RSS feed and displays it as a card-style layout.
<h4>How to use</h4>
<ol>
<li>Add the sBird Latest Feed Card Block in the editor.</li>
<li>Enter the RSS feed URL you want to fetch in the panel setting [Feed URL].</li>
<li>Using the site’s URL instead of the RSS feed URL is also OK</li>
<li>You can choose to show or hide the border.</li>
<li>You can choose a vertical or horizontal layout.</li>
</ol>

sBird Latest Feed Card Block

Display the latest entry from an external RSS feed.

Scriptonite

This is a simple yet powerful plugin to repair your wordpress RSS feed. This plugin will help you if you get an error that looks similar to this:
XML Parsing Error: XML or text declaration not at start of entity 
Location: http://www.yoursite.com/feed/ 
Line Number 2, Column 2: 
-^
If you get this error and have not been able to resolve your feed issues than this plugin is what you need. RSS repair adds a new item to your wordpress tools menu. After you do a core update or theme update and your feed stops working, apply the fix and your feed will be as good as new.
Code sources from: http://wejn.org/stuff/wejnswpwhitespacefix.php.html

Fix My Feed RSS Repair

This is a simple yet powerful plugin to repair your wordpress RSS feed. This plugin will help you if you get an error that looks similar to this:

sBird Latest Feed Card Block vs Fix My Feed RSS Repair