When 2 or more radio buttons are in the same group and you check one of them, the others go automatically in unchecked state. However, when you only uncheck one of the buttons, even if there are only 2, the second one won't go in checked state.
In a scenario where you have 2 button and want to bind the IsChecked property to a property of your ViewModel, you can add converter or additional logic to control the buttons behavior and change their states. You can find attached a sample where this approach is demonstrated.
I hope this information helps.
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