Fix:
In trampoline UnityAppController+ViewHandling.mm change createUnityViewControllerForTVOS to:

- (UnityViewControllerBase*)createUnityViewControllerForTVOS
{
UnityDefaultTVViewController* controller = [[UnityDefaultTVViewController alloc] init];
// This enables game controller use in on-screen keyboard
controller.controllerUserInteractionEnabled = YES;
return controller;
}

To Reproduce:

1. Attach a gamepad to you Apple TV (used Steelseries stratus).
2. Build and run the attached project.
3. Click on any of the input field.
4. Observe that the native keyboard can't be navigated/used with the gamepad (only Apple remote works).

This works in all other native apps I've tested (Search app, Youtube, Bloomberg TV etc..)