Screen contents size and ratio adjustment setting
When an App is set to run at either 16:9 or 16.7:9 aspect screen ration it can be difficult to touch any of the buttons. This is due to the aspect ratio the app has been designed to run in by the developer.
Running the app in 18:9 screen aspect ratio (Full Screen) should allow full use of the application.
You can manually the aspect ratio for each app via the App scaling screens, just choose the option that best fits the app you are trying to use.
Access App scaling by doing the following:
Settings > Display > App scaling