protected function build(ContainerBuilder $container)
{
    $container->register(MyService::class)
        ->setPublic(true)
        ->setArgument('$myEnum', MyEnum::First)
    ;
}

return static function (ContainerConfigurator $configurator): void {
    $configurator->services()->set(MyService::class)
        ->public()
        ->arg('$myEnum', MyEnum::First)
    ;
};

$configurator->services()->set(MyService::class)
    ->arg('$myEnum', MyEnum::First)
;

<?php

namespace App\Service;

enum MyEnum: string
{
    case First = 'first';
    case Second = 'second';
}

<?php

namespace App\Service;

class MyService
{
    public function __construct(MyEnum $myEnum)
    {
    }
}

case null === $value:
case \is_scalar($value):
    return $value;

case null === $value:
case \is_scalar($value):
case $value instanceof \UnitEnum:
    return $value;