When executing this code in xamarin, I get this warning and it does not let me compile the program, someone explain to me why this problem, thank you in advance.
He does not let me compile that warning
Read the little letters that appear in "Salida" say the following:
Here I pause: Are you going to use the emulator that gives you the same Android? Are you going to use the Visual Studio emulator for Android? Are you going to use another emulator?
Considering the lack of details in your question and seeing the output of your execution, I will assume that you have Hyper-V running and you have installed Visual Studio Emulators for Android. With this, you have to go to Tools - > Visual Studio Emulator for Android:
Select the profile you wish to create and "give it play", this will save you time when "debugging" the application. When you do, be sure to select the same profile (on the side of the green arrow).
Recommendations:
Always read the exit, there until it tells you what to do.
Always open the Visual Studio with administrator permissions.
In case you need internet access to your app, this post has the answer: link