You may have noticed issues with websites after upgrading to WordPress 5.5. In this version WordPress stopped using jQuery Migrate which was being used to bridge outdated code in themes and plugins.
This is a good thing in the long run so that developers keep up with modern code and help help avoid security issues.
However if you need some time to fix the outdated code the is a solution by using the plugin Enable jQuery Migrate Helper
With the update to WordPress 5.5, a migration tool known as
jquery-migratewill no longer be enabled by default. This may lead to unexpected behaviors in some themes or plugins who run older code.This plugin serves as a temporary solution, enabling the migration script for your site to give your plugin and theme authors some more time to update, and test, their code.
Enable jQuery Migrate Helper
This plugin will show where issue are to fix but where possible update all themes and plugins.
Additional useful information
https://ithemes.com/wordpress-5-5-breaking-websites-how-to-fix/