RealityKit as a framework to build 3D nonAR apps

Apple has been preparing a replacement for SceneKit, and it's definitely a Reality family – RealityKit, RealityFoundation, Reality Composer (iOS/macOS), Reality Converter, QuickLook, etc. Using RealityKit 2.0, you can create both AR and VR apps. As a tool for prototyping 3D scenes, you need to use Reality Composer. And even despite the lack of such an important feature as .allowsCameraControl, you are now able to make VR apps using RealityKit.

Workaround

Nonetheless, use my code as a starting point to create your own camera control for VR in RealityKit:

import UIKit
import RealityKit

class ViewController: UIViewController {
    @IBOutlet var arView: ARView!
    let buildings = try! Experience.loadScene()
    let camera = PerspectiveCamera()
    var current_X_Angle: Float = 0.0
    var current_Y_Angle: Float = 0.0

    override func viewDidLoad() {
        super.viewDidLoad()
        arView.environment.background = .color(.systemCyan)
        arView.scene.anchors.append(buildings)
        self.camera.position.z = 1
        buildings.children[0].addChild(self.camera)
        self.gestureRecognizer()
    }
    func gestureRecognizer() {
        for gestureRecognizer in [UIPanGestureRecognizer.self,
                                  UIPinchGestureRecognizer.self] {
            if gestureRecognizer == UIPinchGestureRecognizer.self {
                let r = UIPinchGestureRecognizer(target: self,
                               action: #selector(allowCameraControl_01))
                arView.addGestureRecognizer(r)
            }
            if gestureRecognizer == UIPanGestureRecognizer.self {
                let r = UIPanGestureRecognizer(target: self,
                               action: #selector(allowCameraControl_02))
                arView.addGestureRecognizer(r)
            }
        }
    }
    @objc func allowCameraControl_01(recognizer: UIPinchGestureRecognizer) {
        switch recognizer.state {
            case .changed, .ended:
                self.camera.position.z *= 1 / Float(recognizer.scale)
                recognizer.scale = 1.0
            default: break
        }
    }
    @objc func allowCameraControl_02(recognizer: UIPanGestureRecognizer) {
        switch recognizer.state {
            case .changed, .ended:
                let translate = recognizer.translation(in: recognizer.view)
                let angle_X = Float(translate.y / 300) * .pi / 180.0
                let angle_Y = Float(translate.x / 100) * .pi / 180.0
                self.current_X_Angle += angle_X
                self.current_Y_Angle += angle_Y                
                camera.setOrientation(Transform(pitch: current_X_Angle,
                                                  yaw: current_Y_Angle,
                                                 roll: .zero).rotation,
                                      relativeTo: buildings.anchor)
            default: break
        }
    }
}