Don’t freak out – this is because in WordPress 5.5, the jQuery Migrate plugin has been removed and in WordPress 5.6 the jQuery plugin has been updated to the latest version.
Luckily the fixing these problems is simple, there is a plugin you can install to easily manage the jQuery version and enable the jQuery migrate plugin on your website again.
You simply need to play around with the jQuery manager plugin and you should be able to fix all of the issues you are facing. The exact version and settings you require with this plugin will vary depending on the cause of your issues, but you can experiment with the jQuery version and other settings until things start working again on your website.
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