The Security Patches in this update alone are required for the update.
Who wants to run a business on this hosting knowing your stuff can be compromised due to lack of ability to update for existing stable software.

Magento 2.4 will remove support for Elasticsearch 5.x and 6.x, making the default version 7.6.x. Magento 2.4 will also remove MySql search engine, making the elasticsearch engine the default and only option.

This is a must if you wish to host future Magento websites.

Also, Magento 2.4 removes support for MariaDB 10.1. The new standard is 10.4, which brings improved performance.

Link to official documentation: https://devdocs.magento.com/guides/v2.4/release-notes/release-notes-2-4-0-open-source.html#platform-upgrades

Based on the email sent by magento (below), please update the according php versions ASAP if possible.

Kind regards,
Jakab András

Magento, An Adobe Company
A vulnerability has recently been discovered in PHP and we recommend Magento Commerce customers adopt changes to address the issue.
MS-ISAC has issued an alert related to multiple vulnerabilities that could allow for arbitrary code execution and a recommendation that all sites using PHP should update to the latest PHP version ASAP ( full alert is available here).

Since Magento Commerce relies on PHP, we recommend that all Merchants using Magento Commerce review necessary updates for PHP with their hosting provider. We also recommend that Merchants complete this review and any updates by September 30 in order to mitigate the vulnerability and to avoid PCI compliance issues that may go into effect as a result of these vulnerabilities at the end of the month. For those using Magento Commerce on our cloud infastructure, please find specific information on these changes here.

Per the alert, recommended patches for this vulnerability include:

PHP 7.1: <a rel="nofollow noreferrer" href="https://www.php.net/ChangeLog-7.php#7.1.32">https://www.php.net/ChangeLog-7.php#7.1.32</a>

PHP 7.2: <a rel="nofollow noreferrer" href="https://www.php.net/ChangeLog-7.php#7.2.22">https://www.php.net/ChangeLog-7.php#7.2.22</a>

PHP 7.3: <a rel="nofollow noreferrer" href="https://www.php.net/ChangeLog-7.php#7.3.9">https://www.php.net/ChangeLog-7.php#7.3.9</a>

If you would like more information on PHP and recent releases, you can visit PHP’s site. And if you have questions or would like more information on best practices for security, please check out our DevBlog article on Security.