Google made a change that requires you to have a compatible browser installed to complete your account addition.

myViewBoard Whiteboard uses WebViews to help display web content in our app; however, Google no longer allows embedded WebViews as of September 30, 2021.

As users try to sign in to Google from the Embedded Browser (or widget) in our Whiteboard for Windows, Google will block it.

Please see more from the Google Policy: 403_Disallowed Agent