The XAMPP splash page has been removed since the year 2016, so you can’t access it any longer.
You only get the 404 Not Found error when navigating to localhost/xampp/splash.php with the latest XAMPP version.
As of this writing, the XAMPP homepage has been replaced with the dashboard HTML page as follows:
The navigation bar at the top of the dashboard page allows you to navigate to XAMPP guides, PHPinfo page, and PHPMyAdmin application.
The orange administration page under index.php as shown below has also been removed:
There’s no longer a security page for XAMPP because XAMPP was designed for local testing and development environment.
The need to secure XAMPP comes when you want to make it a live/production environment. But it was no longer recommended to use XAMPP for the production environment, so the security page has been removed along with the admin page.
Outdated XAMPP tutorials will show you both the splash and admin page, but you can skip the setup and add your PHP application to the htdocs/ folder right away.