Is this a new TYPO3 installation or did it work previously? What URL are you accessing when you get this error message (you don’t have to include the domain)?
As the documentation says, a non-composer installation of TYPO3 is “now considered out of date, users are strongly encouraged to use the Composer based Installing TYPO3.” I would also highly recommend installing TYPO3 using Composer.
However, even with a non-Composer installation, you will probably get somewhere by following the Composer-based installation guide from the Access TYPO3 via a web browser section.
I am having the same problem with a legacy installation for TYPO3 13.
What I did:
composer create-project typo3/cms-base-distribution typo3 "^13" to create project in /var/www/html/typo3 (works without errors)
Then I just try to access it on my server and I get a 500 error (same result for / or /typo3/install.php).
Looking for some logs I found this in the php-fpm www-error.log:
PHP Fatal error: Uncaught Error: Typed static property TYPO3\CMS\Core\Utility\ExtensionManagementUtility::$packageManager must not be accessed before initialization in /var/www/html/typo3/vendor/typo3/cms-core/Classes/Utility/ExtensionManagementUtility.php:72
Stack trace:
#0 /var/www/html/typo3/vendor/typo3/cms-core/Classes/Utility/GeneralUtility.php(2438): TYPO3\CMS\Core\Utility\ExtensionManagementUtility::resolvePackagePath()
#1 /var/www/html/typo3/vendor/typo3/cms-core/Classes/Controller/ErrorPageController.php(47): TYPO3\CMS\Core\Utility\GeneralUtility::getFileAbsFileName()
#2 /var/www/html/typo3/vendor/typo3/cms-core/Classes/Utility/GeneralUtility.php(2809): TYPO3\CMS\Core\Controller\ErrorPageController->__construct()
#3 /var/www/html/typo3/vendor/typo3/cms-core/Classes/Error/ProductionExceptionHandler.php(63): TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance()
#4 /var/www/html/typo3/vendor/typo3/cms-core/Classes/Error/AbstractExceptionHandler.php(76): TYPO3\CMS\Core\Error\ProductionExceptionHandler->echoExceptionWeb()
#5 [internal function]: TYPO3\CMS\Core\Error\AbstractExceptionHandler->handleException()
#6 {main}
thrown in /var/www/html/typo3/vendor/typo3/cms-core/Classes/Utility/ExtensionManagementUtility.php on line 72
After setting up some remote debugging I found out that there was an exception happening during the Bootstrap process which said something like “could not create file”
So I have redone the file permission for the whole typo3 folder with
chown -R myuser:apache typo3
(or whatever username your server has, mine was apache)