Wrap into Combine (Promise-Future) code with 2 completions/branches?

Question

https://developers.google.com/admob/ios/privacy

class ViewController: UIViewController {

  // Use a boolean to initialize the Google Mobile Ads SDK and load ads once.
  private var isMobileAdsStartCalled = false

  override func viewDidLoad() {
    super.viewDidLoad()

    // Request an update for the consent information.
    UMPConsentInformation.sharedInstance.requestConsentInfoUpdate(with: nil) {
      [weak self] requestConsentError in
      guard let self else { return }

      if let consentError = requestConsentError {
        // Consent gathering failed.
        return print("Error: \(consentError.localizedDescription)")
      }

      UMPConsentForm.loadAndPresentIfRequired(from: self) {
        [weak self] loadAndPresentError in
        guard let self else { return }

        if let consentError = loadAndPresentError {
          // Consent gathering failed.
          return print("Error: \(consentError.localizedDescription)")
        }

        // Consent has been gathered.
        if UMPConsentInformation.sharedInstance.canRequestAds {
          self.startGoogleMobileAdsSDK()
        }
      }
    }
    
    // Check if you can initialize the Google Mobile Ads SDK in parallel
    // while checking for new consent information. Consent obtained in
    // the previous session can be used to request ads.
    if UMPConsentInformation.sharedInstance.canRequestAds {
      startGoogleMobileAdsSDK()
    }
  }
  
  private func startGoogleMobileAdsSDK() {
    DispatchQueue.main.async {
      guard !self.isMobileAdsStartCalled else { return }

      self.isMobileAdsStartCalled = true

      // Initialize the Google Mobile Ads SDK.
      GADMobileAds.sharedInstance().start()

      // TODO: Request an ad.
      // GADInterstitialAd.load(...)
    }
  }
}

I want to move viewDidLoad inner code and startGoogleMobileAdsSDK() as Combine methods which return Future<Error, Never> and/or Future<(), Never>. The problem is UMPConsentInformation.sharedInstance.requestConsentInfoUpdate... may call GADMobileAds.sharedInstance().start() (google ads initialisation) or viewDidLoad may call the same method and I don't know how to handle such branches properly.

In the same time I can't write promise(.success(())) because it may be executed multiple times. How to resolve this issue correctly?