Please note that the MobileAds.Initialize() method is not mandatory so you should be able to load Ads successfully without calling this method. This method is primarily used to reduce load time on your very first Ad request.
Alternatively, you may opt not to call this method at app launch (e.g onCreate) but instead on a later part (e.g after all the views in your launching screen are displayed) before the screen/part where the first Ad request will be sent out.