After upgrading to Visual Studio 16.4 I couldn't deploy an older Xamarin.Forms branch to a Samsung Galaxy Tab S5e. Visual Studio could not deploy the App to the device.

ADB1000: Deployment failed Mono.AndroidTools.RequiresUninstallException: The installed package is incompatible. Please manually uninstall and try again. at Mono.AndroidTools.Internal.AdbOutputParsing.CheckInstallSuccess(String output, String packageName)

After digging around google I found this useful Entry in the Visual Studio Developer Community.

A workaround is available to fix this critical issue:

1. Open Tools -> Android -> Android ADB Command Prompt
2. Run the uninstall command via adb and pass your APK package name. adb uninstall com.yourcompanyname.yourappname
3. Deploy the app through Visual Studio again. This time it should work.