Rule source on GitHub

DowngradeNeverTypeDeclarationRector

Remove "never" return type, add a "@return never" tag instead

-function someFunction(): never
+/**
+ * @return never
+ */
+function someFunction()
 {
 }

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp81\Rector\FunctionLike\DowngradeNeverTypeDeclarationRector;

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