If you are updating an old solution, make sure you change your Android Application project to target Android 10. Otherwise the NuGet package won’t install properly for the Android Application. If you are still using packages.config, you may have to uninstall the packages and install them again after changing target.

You can reference the TipCalc sample here: https://github.com/MvvmCross/MvvmCross-Samples/tree/master/TipCalc