Multiple warnings and an error but the app runs correctly

I am modifying an basic Calc app I found on the web.

I added a CLEAR button with this axml:

Here's the axmal:

<LinearLayout
    android:id="@+id/wrapper4"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/wrapper3"
    android:weightSum="1.0">
 <Button
        android:text="Clear"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/btn0"
        android:layout_weight=".25"

    android:theme="@style/CustomButton"
        style="@style/Widget.AppCompat.Button.Colored"
        android:id="@+id/btnClear" />
</LinearLayout>

And here's the C# code in MainActivity.cs:

Button clr = (Button)FindViewById(Resource.Id.btnClear);

The app compiles but....

Here's some of the many warnings and the error:

Severity Code Description Project File Line Suppression State
Warning Directory obj\Release\MonoAndroid81\android/assets contains Xamarin.Android.Arch.Lifecycle.Common.dll but no debug symbols file was found. 0
Warning Directory obj\Release\MonoAndroid81\android/assets contains Xamarin.Android.Arch.Core.Common.dll but no debug symbols file was found. 0
Warning Directory obj\Release\MonoAndroid81\android/assets contains Java.Interop.dll but no debug symbols file was found. 0
Error ADB0010: Failure [INSTALL_FAILED_NO_MATCHING_ABIS: Failed to extract native libraries, res=-113]
at Mono.AndroidTools.Internal.AdbOutputParsing.CheckInstallSuccess(String output, String packageName) in E:\A_work\122\s\External\androidtools\Mono.AndroidTools\Internal\AdbOutputParsing.cs:line 338
at Mono.AndroidTools.AndroidDevice.<>c__DisplayClass94_0.b__0(Task1 t) in E:\A\_work\122\s\External\androidtools\Mono.AndroidTools\AndroidDevice.cs:line 746 at System.Threading.Tasks.ContinuationTaskFromResultTask1.InnerInvoke()
at System.Threading.Tasks.Task.Execute() 0
Error CS0117 'Resource.Id' does not contain a definition for 'btnClear' Calc5 P:\C#\Android\Calc5\Calc5\MainActivity.cs 40 Active

I've deleted the Release dir; rebooted both the phone and the computer.

After I run Build and then Deploy (ignoring the errors) I get a signed.apk file in the release dir. I can copy it to the phone and install it there and it runs correctly.

I would like any input as to why I'm getting these errors and warnings.

RON