Xamarin 4.8.0.576; Xamarin.Android 8.1.0.13
There used to be a way to tell Xamarin.Android which ABIs to build for. I don't see that any more.
(Looking in Project Properties / Android Options.)
My (very old) project seems to be only building for ARM; not building for x86 to run emulator.
(Tested by building with both "minimum" and "target" set to "API-23",
then attempting to run on two different emulators that Visual Studio + Xamarin install created,
API-23 on ARM (VisualStudio_android-23_arm_phone), which worked (but very slow of course),
API-23 on x86 (VisualStudio_android-23_x86_phone), with result "INSTALL_FAILED_NO_MATCHING_ABIS ".)
How solve?
IMPORTANT: If I create a new Android Blank App, that works correctly. But somehow my old project,
that was built using Xamarin Studio (though I have not tried in the past six months,
and now I am on a different PC), is not deployable to x86 Android emulator using Visual Studio.