Since J4 the escape function in \libraries\src\MVC\View\HtmlView.php - Line 233 includes single quotes by passing the ENT_QUOTES flag to htmlspecialchars()

The escape method is used to strip html from the feed item title by first escaping the item title.
Then the title is decoded by html_entity_decode using the ENT_COMPAT flag
This causes the html-single-quote-entity (') to remain in the title.

I guess the title is amp_replaced on parsing the rss feed causing the ' to become ' in the final output.

Steps to reproduce the issue

Create an article in category EXAMPLE (category id = 1) with single quotes in the title.
title = This is a 'test' article

Display a feed from this category index.php?option=com_content&view=category&id=1&format=feed&type=rss

Expected result

Well formed RSS feed which shows this title element:
<title>This is a 'test' article</title>

Actual result

<title>This is a &amp;#039;test&amp;#039; article</title>

System information (as much as possible)

Joomla 4.3.1
PHP 8.1.10

Additional comments

Changing the flag to ENT_QUOTES in the html_entity_decode function fixes the issue.

Current situation:

$title = "This is a 'test' article";

$title = htmlspecialchars($title, ENT_QUOTES, 'UTF-8');
echo $title;

$title = html_entity_decode($title, ENT_COMPAT, 'UTF-8');
echo $title;

This is a 'test' article
This is a 'test' article

Fixed:

$title = "This is a 'test' article";

$title = htmlspecialchars($title, ENT_QUOTES, 'UTF-8');
echo $title;

$title = html_entity_decode($title, ENT_QUOTES, 'UTF-8');
echo $title;

This is a 'test' article
This is a 'test' article