Thanks for posting.
When I try to access Google Calendar from the web viewer in FileMaker Go, I am getting the same message regarding viewing as a mobile site. The Web Viewer in FileMaker uses Apple’s Web Kit, which is not a fully functional browser. The issue is being caused by Google Calendar making a call unsupported by the Web Kit, causing Google to recognize the device as an iPad, redirecting to a mobile version. I’ve reproduced this exact issue in the free app “WebPresenter” where the same message occurs. The WebPresenter is another app that uses the Apple Web Kit.