Composer install gives Uncaught TypeError – PHP Versions

You could try going to illuminate/log/Logger.php and adding use MonologLogger as Monolog; at the beginning of the file. After that, change the constructor from this:

    /**
     * Create a new log writer instance.
     *
     * @param  PsrLogLoggerInterface  $logger
     * @param  IlluminateContractsEventsDispatcher|null  $dispatcher
     * @return void
     */
    public function __construct(LoggerInterface $logger, Dispatcher $dispatcher = null)
    {
        $this->logger = $logger;
        $this->dispatcher = $dispatcher;
    }

to this:

    /**
     * Create a new log writer instance.
     *
     * @param  MonologLogger  $logger
     * @param  IlluminateContractsEventsDispatcher|null  $dispatcher
     * @return void
     */
    public function __construct(Monolog $logger, Dispatcher $dispatcher = null)
    {
        $this->logger = $logger;
        $this->dispatcher = $dispatcher;
    }