The package doctrine/reflection is no longer used by Drupal core.

The doctrine/reflection package is no longer used by Drupal core, because the package is abandoned and is no longer maintained. The code from the package that Drupal relies on has been copied to Drupal\Component\Annotation\Doctrine. To leverage the same code in contrib or custom code you can update the namespaces:

Before: Doctrine\Common\Reflection\StaticReflectionParser
After: Drupal\Component\Annotation\Doctrine\StaticReflectionParser

Before: Doctrine\Common\Reflection\ClassFinderInterface
After: Drupal\Component\ClassFinder\ClassFinderInterface

The doctrine/reflection package will stay in Drupal 9 and will be removed before Drupal 10.0.0. However, if you want full compatibility with all versions of PHP, custom and contrib code will need to be refactored sooner as the package is not compatible with PHP 8.1.