core PHP 8.1 not supported

`# php8.1 --version`

PHP 8.1.0 (cli) (built: Nov 25 2021 20:22:03) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.1.0, Copyright (c) Zend Technologies
    with Zend OPcache v8.1.0, Copyright (c), by Zend Technologies

PHP Fatal error: During inheritance of ArrayAccess: Uncaught ErrorException: Return type of flight\util\Collection::offsetExists($offset) should either be compatible with ArrayAccess::offsetExists(mixed $offset): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/chroot/home/test/root/include/flight/util/Collection.php:102

Errors:

Fatal error: During inheritance of ArrayAccess: Uncaught ErrorException: Return type of flight\util\Collection::offsetExists($offset) should either be compatible with ArrayAccess::offsetExists(mixed $offset): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/chroot/home/test/root/include/flight/util/Collection.php:102 Stack trace: #0 /var/chroot/home/test/root/include/flight/util/Collection.php(15): flight\Engine->handleError() #1 /var/chroot/home/test/root/include/flight/core/Loader.php(194): require('...') #2 /var/chroot/home/test/root/include/flight/net/Request.php(147): flight\core\Loader::loadClass() #3 /var/chroot/home/test/root/include/flight/core/Loader.php(125): flight\net\Request->__construct() #4 /var/chroot/home/test/root/include/flight/core/Loader.php(81): flight\core\Loader->newInstance() #5 /var/chroot/home/test/root/include/flight/Engine.php(101): flight\core\Loader->load() #6 /var/chroot/home/test/root/include/flight/Engine.php(311): flight\Engine->__call() #7 /var/chroot/home/test/root/include/flight/core/Dispatcher.php(198): flight\Engine->_start() #8 /var/chroot/home/test/root/include/flight/core/Dispatcher.php(144): flight\core\Dispatcher::invokeMethod() #9 /var/chroot/home/test/root/include/flight/core/Dispatcher.php(49): flight\core\Dispatcher::execute() #10 /var/chroot/home/test/root/include/flight/Engine.php(92): flight\core\Dispatcher->run() #11 /var/chroot/home/test/root/include/flight/core/Dispatcher.php(198): flight\Engine->__call() #12 /var/chroot/home/test/root/include/flight/Flight.php(77): flight\core\Dispatcher::invokeMethod() #13 /var/chroot/home/test/root/index.php(70): Flight::__callStatic() #14 {main} in /var/chroot/home/test/root/include/flight/util/Collection.php on line 15

Same source/project work with PHP 8.0.14. but not with PHP 8.1.

Best, M.