Filesystem error: Impossible to create the root directory

I configured a local network drive like so:

    'disks' => [

        'local' => [
            'driver' => 'local',
            'root' => storage_path('app'),
        ],

        'rDrive' => [
            'driver' => 'local',
            'root'   => 'R:',
        ]
    
    ]

Using php artisan tinker, I get a directory listing as expected with this: Storage::disk('rDrive')->directories();

When I try the same test line or other use of the drive in my project, I get the Whoops error:

Exception in Local.php line 106:
Impossible to create the root directory "R:".

I am struggling to make use of network paths in a windows development environment.

Network drives and symlinks work fine from the Windows CLI using php artisan tinker. The same code does not work in the project running on a WAMP server.