Aimy Captcha-Less Form Guard v11.3 provides a workaround for a Joomla! 4.0 compatibility issue with PHP 8.0.

There’s a compatibility issue with Joomla! 4.0 and PHP 8.0 that affects the functionality of Aimy Captcha-Less Form Guard. The issue will likely be fixed in Joomla! 4.0.5 - however, meanwhile Aimy Captcha-Less Form Guard comes with a workaround.

Thanks to Pascal for both reporting the issue and providing the workaround!