Login page broken with no content

Nextcloud version (eg, 20.0.5): replace me
Operating system and version (eg, Ubuntu 20.04): Manjaro 21.0.4
Apache or nginx version : Nginx 1.19.0
PHP version: 8.0.5

The issue you are facing:

I setup nextcloud earlier today and after completing the setup, I’m brought to a broken login screen.

the following shows in the nextcloud log (/var/log/nextcloud/nextcloud.log)

{"reqId":"olFgT7NxG6xU3q59mYCg","level":3,"time":"2021-05-19T04:42:38+00:00","remoteAddr":"192.168.2.250","user":"--","app":"PHP","method":"GET","url":"/js/core/merged-template-prepend.js?v=fd2e34f8-0","message":{"Exception":"Error","Message":"session_regenerate_id(): Session ID cannot be regenerated when there is no active session at /usr/share/webapps/nextcloud/lib/private/Session/Internal.php#137","Code":0,"Trace":[{"function":"onError","class":"OC\\Log\\ErrorHandler","type":"::"},{"file":"/usr/share/webapps/nextcloud/lib/private/Session/Internal.php","line":137,"function":"session_regenerate_id"},{"file":"/usr/share/webapps/nextcloud/lib/private/Session/CryptoSessionData.php","line":161,"function":"regenerateId","class":"OC\\Session\\Internal","type":"->"},{"file":"/usr/share/webapps/nextcloud/lib/private/Session/CryptoSessionData.php","line":90,"function":"regenerateId","class":"OC\\Session\\CryptoSessionData","type":"->"},{"file":"/usr/share/webapps/nextcloud/lib/private/Session/CryptoSessionData.php","line":66,"function":"initializeSession","class":"OC\\Session\\CryptoSessionData","type":"->"},{"file":"/usr/share/webapps/nextcloud/lib/private/Session/CryptoWrapper.php","line":113,"function":"__construct","class":"OC\\Session\\CryptoSessionData","type":"->"},{"file":"/usr/share/webapps/nextcloud/lib/base.php","line":420,"function":"wrapSession","class":"OC\\Session\\CryptoWrapper","type":"->"},{"file":"/usr/share/webapps/nextcloud/lib/base.php","line":639,"function":"initSession","class":"OC","type":"::"},{"file":"/usr/share/webapps/nextcloud/lib/base.php","line":1076,"function":"init","class":"OC","type":"::"},{"file":"/usr/share/webapps/nextcloud/index.php","line":35,"args":["/usr/share/webapps/nextcloud/lib/base.php"],"function":"require_once"}],"File":"/usr/share/webapps/nextcloud/lib/private/Log/ErrorHandler.php","Line":92,"CustomMessage":"--"},"userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:88.0) Gecko/20100101 Firefox/88.0","version":"21.0.1.1"}

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

<?php
$CONFIG = array (
  'datadirectory' => '/var/lib/nextcloud/data',
  'logfile' => '/var/log/nextcloud/nextcloud.log',
  'apps_paths' => 
  array (
    0 => 
    array (
      'path' => '/usr/share/webapps/nextcloud/apps',
      'url' => '/apps',
      'writable' => false,
    ),
    1 => 
    array (
      'path' => '/var/lib/nextcloud/apps',
      'url' => '/wapps',
      'writable' => true,
    ),
  ),
  'instanceid' => REDACTED,
  'passwordsalt' => REDACTED,
  'secret' => REDACTED,
  'trusted_domains' => 
  array (
    0 => REDACTED,
  ),
  'dbtype' => 'pgsql',
  'version' => '21.0.1.1',
  'overwrite.cli.url' => REDACTED,
  'dbname' => 'nextcloud',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'dbuser' => 'nextcloud',
  'dbpassword' => REDACTED,
  'installed' => true,
);

Nginx error log was empty in /var/log/nginx/error.log