Rule source on GitHub

DowngradeUnionIntersectionRector

Remove the union type with intersection, use docblock based

 final class SomeClass
 {
-    public (A&B)|C $foo;
+    /**
+     * @var (A&B)|C
+     */
+    public $foo;
 }

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp82\Rector\Class_\DowngradeUnionIntersectionRector;

return RectorConfig::configure()
    ->withRules([
        DowngradeUnionIntersectionRector::class,
    ]);