$someObject = new SomeExampleClass;
-$someObject->someMethod();
+$someObject->someMethod(true);

 class MyCustomClass extends SomeExampleClass
 {
-    public function someMethod()
+    public function someMethod($value = true)
     {
     }
 }

Configure your rector.php:

<?php

use PHPStan\Type\ObjectType;
use Rector\Arguments\Rector\ClassMethod\ArgumentAdderRector;
use Rector\Arguments\ValueObject\ArgumentAdder;
use Rector\Config\RectorConfig;

return RectorConfig::configure()
    ->withConfiguredRule(ArgumentAdderRector::class, [
        new ArgumentAdder('SomeExampleClass', 'someMethod', 0, 'someArgument', true, new ObjectType('SomeType')),
    ]);

SETS:  PHP 8.0 symfony/* 3.2 symfony/* 3.3 symfony/* 4.2 symfony/* 4.3