symfony, var-folder as symlink does not work on apache due to wrong vendor-includes

I have an empty symfony, installed via composer.json, apache-pack and api-platform included (see file below).

Environment

We need to offer the var-folder as a symlink.

  • App-Folder: /app
  • Var-Folder: /contents/var

The app-folder structure results in:

[...] 
templates 
var -> /contents/var 
vendor

Problem

Symfony creates classes in var/cache, which include vendor-classes like this:

include_once dirname(__DIR__, 4).'/vendor/symfony/kernel/ErrorHandler.php';

The problem is, that __ DIR __ returns the source-path of the symlink, not the target app-path, so the class cannot be found:

Warning: include_once(/contents/vendor/symfony/kernel/ErrorHandler.php): Failed to open stream: No such file or directory

So it says vendor is in
/contents/vendor instead of
/app/vendor

If DIR would return the app-path, everything would be fine:
/app/vendor/symfony/kernel/ErrorHandler.php

Question

Does anybody know how to solve this? It is NOT possible to change the environment due to a gitlab-setup which can’t be changed by us.

composer.json

{
    "type": "project",
    "license": "proprietary",
    "minimum-stability": "stable",
    "prefer-stable": true,
    "require": {
        "php": ">=8.1",
        "ext-ctype": "*",
        "ext-iconv": "*",
        "api-platform/core": "^3.2",
        "doctrine/doctrine-bundle": "^2.10",
        "doctrine/doctrine-migrations-bundle": "^3.2",
        "doctrine/orm": "^2.16",
        "nelmio/cors-bundle": "^2.3",
        "phpdocumentor/reflection-docblock": "^5.3",
        "phpstan/phpdoc-parser": "^1.24",
        "symfony/apache-pack": "^1.0",
        "symfony/asset": "6.3.*",
        "symfony/console": "6.3.*",
        "symfony/dotenv": "6.3.*",
        "symfony/expression-language": "6.3.*",
        "symfony/flex": "^2",
        "symfony/framework-bundle": "6.3.*",
        "symfony/property-access": "6.3.*",
        "symfony/property-info": "6.3.*",
        "symfony/runtime": "6.3.*",
        "symfony/security-bundle": "6.3.*",
        "symfony/serializer": "6.3.*",
        "symfony/twig-bundle": "6.3.*",
        "symfony/validator": "6.3.*",
        "symfony/yaml": "6.3.*"
    },
    "require-dev": {
        "symfony/maker-bundle": "^1.51"
    },
    "config": {
        "allow-plugins": {
            "php-http/discovery": true,
            "symfony/flex": true,
            "symfony/runtime": true
        },
        "sort-packages": true
    },
    "autoload": {
        "psr-4": {
            "App\": "src/"
        }
    },
    "autoload-dev": {
        "psr-4": {
            "App\Tests\": "tests/"
        }
    },
    "replace": {
        "symfony/polyfill-ctype": "*",
        "symfony/polyfill-iconv": "*",
        "symfony/polyfill-php72": "*",
        "symfony/polyfill-php73": "*",
        "symfony/polyfill-php74": "*",
        "symfony/polyfill-php80": "*",
        "symfony/polyfill-php81": "*"
    },
    "scripts": {
        "auto-scripts": {
            "cache:clear": "symfony-cmd",
            "assets:install %PUBLIC_DIR%": "symfony-cmd"
        },
        "post-install-cmd": [
            "@auto-scripts"
        ],
        "post-update-cmd": [
            "@auto-scripts"
        ]
    },
    "conflict": {
        "symfony/symfony": "*"
    },
    "extra": {
        "symfony": {
            "allow-contrib": "true",
            "require": "6.3.*"
        }
    }
}