Projeto apresenta falhas quando criado

O Emulador Accelerated tenta iniciar, mas nada acontece, a tela só fica na parte preta. Quando eu fecho o emulador, mostra uma mensagem dizendo que houve erro de implementação.

Erro    CS0103    O nome "InitializeComponent" não existe no contexto atual    Teste2.Android, Teste2.UWP    C:\Users\Leonardo\source\repos\Teste2\Teste2\Teste2\MainPage.xaml.cs    14    Ativo

Aviso        The $(TargetFrameworkVersion) for Xamarin.Forms.Platform.Android.dll (vv8.0) is greater than the $(TargetFrameworkVersion) for your project (v7.1). You need to increase the $(TargetFrameworkVersion) for your project.    Teste2.Android    C:\Users\Leonardo\source\repos\Teste2\Teste2\Teste2.Android\Teste2.Android.csproj

Aviso        The $(TargetFrameworkVersion) for Xamarin.Forms.Platform.dll (vv8.0) is greater than the $(TargetFrameworkVersion) for your project (v7.1). You need to increase the $(TargetFrameworkVersion) for your project.    Teste2.Android    C:\Users\Leonardo\source\repos\Teste2\Teste2\Teste2.Android\Teste2.Android.csproj

Aviso        The $(TargetFrameworkVersion) for FormsViewGroup.dll (vv8.0) is greater than the $(TargetFrameworkVersion) for your project (v7.1). You need to increase the $(TargetFrameworkVersion) for your project.    Teste2.Android    C:\Users\Leonardo\source\repos\Teste2\Teste2\Teste2.Android\Teste2.Android.csproj