Installtool gives status 404 when installPassword is not set in LocalConfiguration.php
The installtool gives a 404 status when the installPassword key is not set in the LocalConfiguration file.
An error message regarding the missing key would be more helpful in this case, I think.
Maintenance Middleware won't handle the request when no installtool password is set:
public/typo3/sysext/install/Classes/Middleware/Maintenance.php:242 causing a 404.
Reproducable in version 10.2 and higher.