Psalm and PHPStan unable to read Symfony entity string:class

Easiest way to fix this is to use \EntityClass::class instead of a string 'MyApp:EntityClass' however I would like to avoid that.

You already wrote the recommended answer. Using shortname alias is deprecated since doctrine/orm v2.10. It'll probably be removed in v3.0. You should consider upgrading.

That said, this is the only sustainable solution.

$repository = $this->em->getRepository(EntityClass::class);

Install phpstan/phpstan-doctrine

Using phpstan without phpstan-doctrine is not recommended (while interpreting types of a doctrine entity). Install the phpstan extension phpstan/phpstan-doctrine and configure it. It interpretes types of QueryBuilder and Repository inside your project; like EntityManager::getReposiotry(EntityClass::class):

composer require --dev phpstan/phpstan-doctrine

# phpstan.neon
parameters:
    doctrine:
        objectManagerLoader: tests/object-manager.php

Optional: automatic refactoring

That said, you really should update your code base. To ease that process, you could use rector using the EntityAliasToClassConstantReferenceRector. Correctly configured, you're done in seconds.

composer require --dev rector/rector

// rector.php

<?php

declare(strict_types=1);

use Rector\Config\RectorConfig;
use Rector\Doctrine\Rector\MethodCall\EntityAliasToClassConstantReferenceRector;

return static function (RectorConfig $rectorConfig): void {
    $rectorConfig->phpstanConfig(__DIR__.'/phpstan.neon');

    $rectorConfig->ruleWithConfiguration(EntityAliasToClassConstantReferenceRector::class, [
        EntityAliasToClassConstantReferenceRector::ALIASES_TO_NAMESPACES => [
            'MyApp' => 'App\Entity',
        ]
    ]);
};