App\Command\InitCommand.php

<?php

namespace App\Command;

use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Output\OutputInterface;

class InitCommand extends Command
{
    protected static $defaultName = 'init';

    protected function configure()
    {
        $this
            // the short description shown while running "php bin/console list"
            ->setDescription('Creates a new user.')

            // the full command description shown when running the command with
            // the "--help" option
            ->setHelp('This command allows you to create a user...');
    }

    protected function execute(InputInterface $input, OutputInterface $output)
    {
        return Command::SUCCESS;
    }
}

cli.php

#!/usr/bin/env php
<?php
// application.php

require __DIR__.'/vendor/autoload.php';

use Symfony\Component\Console\Application;
use App\Command\InitCommand;

$application = new Application();

$application->add(new InitCommand());
$application->run();

gistfile1.txt

{
    "name": test"",
    "description": "CLI test",
    "type": "cli",
    "license": "MIT",
    "authors": [
        {
            "name": "Stephane Erard",
            "email": "stephane.erard.se@gmail.com"
        }
    ],
    "require": {
        "symfony/console": "^5.2"
    },
    "autoload": {
        "psr-0": {
            "App\\": "src/"
        }
    }
}

gistfile2.txt

PS C:\code\frenchex2\vagranti_i2.php> php .\cli.php
PHP Fatal error:  Uncaught Error: Class "App\Command\InitCommand" not found in C:\code\frenchex2\vagranti_i2.php\cli.php:12
Stack trace:
#0 {main}
  thrown in C:\code\frenchex2\vagranti_i2.php\cli.php on line 12