Hi @JotaJotaFdez,
Thank you for reaching out to us. WordPress updated the jQuery version in the version 5.5 which could break the plugins that are using an older version of jQuery. There are no known breaking changes in X, Pro, or Cornerstone. Given the time since WordPress 5.5 was released and all the sites we’ve seen update successfully, we consider this to be a safe update.
First, make sure all your themes and plugins are running the latest versions. If you are still having issues we would advise working through the suggestions in our Troubleshooting Common Issues article.
You can get a hint of whether or not there is a jQuery issue by opening your browser’s developer tools and looking for any errors in the console. Sometimes this will point you to custom code, or a plugin that isn’t working correctly.
For more details please see WordPress 5.5 Considerations
Hope this helps!