WordPress just released its second major update on August 11, which offers many features and user interface improvements, including the Gutenberg Block Editor, which can be used to build your website. But unfortunately, the update has made ten thousands of broken sites, An issue with how the themes handle pagination and WordPress disabling jquery migrate by default caused other websites to crash after updating to 5.5.
why WordPress version 5.5 breaks plugins
WordPress uses a javascript library called jQuery Migrate, and this javascript library acts as a bridge for older code to function on WordPress. So when users use older WordPress themes, especially those that are no longer being updated, compatibility issues have finally crept up, and with WordPress 5.5 jquery-migrate is no longer be enabled by default.
after updating to WordPress 5.5 you will release that with the number of plugins(Classic Editor and Yoast etc) installed on your CMS (WordPress) will not be working. with Yoast SEO will see that the focus keyphrase wont be working
How to fix WordPress version 5.5 issues
WordPress has released a plugin that will restore the jQuery Migrate JavaScript library and return full functionality to the website.The name of the plugin is called Enable jQuery Migrate Helper.