In October 2021, DuoSecurity will be releasing a new version 4 of their Duo Mobile application for Apple and Android devices. There are some major design differences which may cause some confusion, notably the position of the Approve and Deny Buttons. Here is an image showing the differences.
The other major changes revolve around the sign up process which is only necessary when installing on a new phone. For more information, please take a look at DuoSecurity's website or watch their video on the new version of their mobile app.