Steps to reproduce the issue

Fresh install Joomla_4.0.0-alpha12-Alpha-Full_Package.tar.bz2
Browse to site, 500 error. Server error log reports:

FastCGI sent in stderr: "PHP message: PHP Fatal error: require(): Failed opening required '/var/www/html/development/4/libraries/autoload_psr4.php' (include_path='.:/usr/share/php') in /var/www/html/development/4/libraries/namespacemap.php on line 94" while reading response header from upstream, client: ::1, server: _, request: "GET /development/4/installation/index.php HTTP/1.1", upstream: "fastcgi://unix:/var/run/php/php7.3-fpm.sock:", host: "localhost"

Expected result

installer page

Actual result

500 error

System information (as much as possible)

Ubuntu 19.10
PHP 7.3.11
NGINX 1.16.1

Additional comments

Creating a symlink from /libraries/vendor/composer/autoload_psr4.php into /libraries resolves the issue.