Unfortunately, older versions of these languages become deprecated and are unsupported once they reach end-of-life. As WordPress evolves with greater functionality, performance and security, your platform must also keep up-to-date. For several years now, WordPress has been using outdated versions of the jQuery library. There are now too many security exploits and performance issues for WordPress to continue to support old versions of jQuery. However, with the migration to newer versions of jQuery comes great risk. Many sites were built with plugins and themes utilizing components specific to the old jQuery versions. Therefore, once jQuery is updated, site functionality could break or even worse, the whole site could go down. Appropriate planning is required when performing the update to minimise site downtime.
Upgrade to WordPress 5.7! There is a three-step plan to upgrade jQuery and WordPress 5.7 is the final step. The plan has been:
WordPress 5.5: Remove the jQuery Migrate 1.x script. (August 2020)
WordPress 5.6: Update to the latest jQuery, jQuery UI, and jQuery Migrate scripts. (December 2020)
WordPress 5.7: Remove the jQuery Migrate script. (March 2021)
With this, the minimum recommended PHP version for the latest WordPress update is now PHP 7.4 or higher. This is preparation for the recently developed PHP 8. It is important that you plan the upgrade to minimise downtime and mitigate any broken site functionality.