I've been developing in symfony for many years.   In an attempt to upgrade an older symfony app to symfony 6, I recently tried to setup the symfony demo app in symfony6/PHP8.1, without success.   Although the symfony demo command doesn't work, there is a symfony demo page that appears to have been updated  <https://github.com/symfony/demo>, requiring PHP 8 or better.   A quick git clone brought the app down, and a 'composer update' made sure everything was up to date.

The website sort of works, but looks terrible.   Checking the console in a chrome browse reveals that indicates that the integrity attribute for multiple /build resources is off, and so it blocks the .css file from loading.   I suspect there is a character or two off in the .css files as git brings them down off github.

But integrity checking should be disablable, by changing the .enableIntegrityHashes(Encore.isProduction()) line in /webpack.config.js, at least so says <https://symfony.com/doc/current/frontend/encore/installation.html>     My development environment is set to dev, so this shouldn't even occur at all, but even when forcing the line above in webpack.config.js to be enableIntegrityHashes(false), the integrity checking keeps being rendered.  This apparently traces to encore_entry_link_tags() in base.html.twig.