TYPO3 Core

With https://docs.typo3.org/c/typo3/cms-core/main/en-us/Changelog/12.1/Feature-98957-RespectWrite-protectedSettingsphpInInstallTool.html the settings.php can be readonly.

But when I login into the Install Tool, the Ajax call

/typo3/install.php?install[controller]=layout&install[context]=&install[action]=executeSilentConfigurationUpdate

throws the following error:

Core: Exception handler (WEB: BE): RuntimeException, code #1346323822, file /var/www/marketplace-test.jobroute
r.com/releases/64/vendor/typo3/cms-core/Classes/Configuration/ConfigurationManager.php, line 390: config/system/settings.php is not writable. - {"mode":"WEB","application_mode":"BE","exception_class":"RuntimeException","exception_code":13
46323822,"file":"/var/www/example.com/vendor/typo3/cms-core/Classes/Configuration/ConfigurationManager.php","line":390,"message":"config/system/settings.php is not writable.","request_url":"https://example.com/typo3/install.php?install[controller]=layout&install[context]=&install[action]=executeSilentConfigurationUpdate","exception":null}