Starting in version 5.5, WordPress changed how they handled jQuery:
- WordPress v5.5 - jQuery Migrate plugin removed. jQuery Migrate allowed JavaScript code using earlier jQuery versions to remain compatible with the jQuery 1.12.4 included with WordPress v5.5.
- WordPress v5.6 - the jQuery version included with WordPress was upgraded from 1.12.4 to 3.5.1, but WordPress released a jQuery Migration plugin to restore compatibility with older versions of jQuery.
- WordPress v5.7 - jQuery Migrate support will be disabled. WordPress themes and plugin which still rely on outdated versions of jQuery will most likely experience issues.
Many popular WordPress theme and plugin developers track upcoming WordPress updates and test their software against newer WordPress versions to ensure compatibility. Future compatibility is one of the benefits of purchasing an actively developed premium WordPress theme or plugin.
In the future, if a website needs to use a theme or plugin released before WordPress 5.5 (August 11, 2020), jQuery compatibility should be considered.