This allows to use all existing Annotations as PHP8 Attributes and makes the ReflectionService pick up attributes like annotations.
Hence all is*AnnotatedWith() and *Annotation() methods will return attribute classes as if they were annotations.

#[Flow\Scope("singleton")]
class MyClass {

    /**
     * @var LoggerInterface
     */
    #[Flow\Inject]
    protected $logger;

Note though, that this means a class that has both annotation and the equal attribute will behave as if all annotations were duplicated.

Also, in case you manually instanciated an Annotation class, you need to adjust to the changed constructor, which no longer takes a named array, but the list of actual properties.
In most cases instead of new Flow\Inject($args) you can probably do new Flow\Inject(...$args) with PHP8 and named parameters.

For Doctrine Annotations - see doctrine/orm#8266 which will be available with 2.9