CI in a Linux environment setup

I tried the .htaccess file on CI_3.1.10 and it worked OK.

I notices that the Routes file has the following and no doubt accounts for why the Splash page is not appearing.

$route['default_controller'] = 'Home/index'; // to
$route['default_controller'] = 'welcome'; // shows the same 404 error page not found

Please try remming the second redirection because it overrides the original redirection to the Home controller.

And don't forget to use the following .htaccess script:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L]

That should render the Splash page and I find it is far better to start with something (Hello world) and add script until failure occurs. It is a nightmare starting with something that does not work.

Once working experiment with different debug options.