Camera Transition Not Working in Unreal Engine 5

I am assuming your ACameraManager inherits from Epic’s APlayerCameraManager?

In that case, your constructor doesn’t call the parent constructor which means you’re missing a bunch of settings and components.
You should go with:

ACameraManager::ACameraManager(const FObjectInitializer& ObjectInitializer)
    : Super(ObjectInitializer)
{
    PrimaryActorTick.bCanEverTick = true;
}

Running further with my assumption, I’m a bit confused about PlayerController->SetViewTarget(NewCamera); as this will just call back ACameraManager::SetViewTarget() which is not inherently wrong but… just curious.

Or maybe my assumption was wrong?

If that is the case you might check your actual APlayerCameraManager and see if it is valid. (because APlayerController::SetViewTarget() will fail silently if there is no valid camera manager)