Visual Studio let’s you create the keystore when distributing your Android App. If you created your Android keystore directly inside Visual Studio it doesn’t tell you where it saved it. You can find it here on Windows:
C:\Users\%username%\AppData\Local\Xamarin\Mono for Android\Keystore
Source: https://docs.microsoft.com/en-us/xamarin/android/deploy-test/signing/keystore-signature?tabs=windows