So with Visual Studio 2019, I built just Hello World app , deployed with ADHOC signing and put the APK on my server hit the site with an 6.0.1 android device "app not installed" on Android 7.1 installs fine .... now I have the app build properites minimum version set android 5.1 target 8.1... same as an app I am developing on Android Studio that will install fine on both devices.

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Took some research to figure out Xamarian and Android you have to create atleast the ADhoc signing or you get the Corrupt or Parser error depending on android version. So I assume there is some other tweak I need for VS 2019 Xamarian to make simple deployment that has teh target span actually install across entire span?

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Now I will admit I tried back in the Day with VS 2017 android development and went running to Android Studio because Android seemed to just work (Even though I was way more comfortable with C# and VS compared to Java and Android Studio)... but great strides VS 2019 has made , if we did android development outside of just one app I might actually consider VS 2019 now.