Drupal is very hot on attributes, has fiber support, uses readonly (a PHP 8.2 feature) extensively, enums are used -- overall it's fairly up to date.

Symfony also does a great job adding polyfills way ahead of a PHP release , eg https://github.com/symfony/polyfill-php84

Yes, and this is incredibly annoying. Many packages add them as a dependency, and then you get subtle bugs because of it. Or worse, they add a dependency for the polyfill that is related to an extension and suffer performance issues when the extensions are not installed; yet no warning is output.