The Esri.ArcGISRuntime.Xamarin.Android package does not currently support building for the arm64-v8a or x86_64 architectures. Please uncheck these options in Project Settings -> Android Options -> Advanced -> Supported architectures.
i am nearly to finish this application.how to solve this on android.
We plan to add support for the arm64-v8a architecture in the upcoming release of ArcGIS Runtime SDK for .NET (v100.3). Support for x86_x64 is under consideration for a future release.
As the build error states, you need to turn off targeting the two 64-bit options. Your app will still run fine on 64bit devices.
As Mike mentioned, the next release will add the ARM v8 option, but it really doesn't matter too much, unless you are also referencing another component that doesn't provide ARMv7 support (almost all do)