When using getAttributes() with specific attribute class and flags, flag 0 will return just matching attributes with specified class, and 2 will return matching attributes with specified class and children of that class:
<?php
    #[Attribute(\Attribute::TARGET_CLASS)]
    class SomeAttribute {}
    #[Attribute(\Attribute::TARGET_CLASS)]
    class ChildAttribute extends SomeAttribute {}
    #[SomeAttribute]
    #[SomeChildAttribute]
    class SomeClass {}
    $rc = new ReflectionClass(SomeClass::class);
    $r_atts = $rc->getAttributes(SomeAttribute::class, 0); echo json_encode(array_map(fn(ReflectionAttribute $r_att) => $r_att->getName(), $r_atts)), PHP_EOL;
    $r_atts = $rc->getAttributes(SomeAttribute::class, 2); echo json_encode(array_map(fn(ReflectionAttribute $r_att) => $r_att->getName(), $r_atts)), PHP_EOL;
?>
output:
["SomeAttribute"]
["SomeAttribute","ChildAttribute"]