Blank screen when adding a Google account

it may take some time once the email has been added to display anything. By time, I'm talking minutes, nor more than 15 max depending on your connection. Its best to connect over wifi to make the process go faster. If you close and reopen the app (Force an app to close in iOS - Apple Support), this puts a pause on the sync service and then reinitiates it again when you open the Mail app. Its not advised normally, you should never close your apps, but it may at least show the app doing something.