I need help with what should be a very simple problem. I am new to both xaml and Xamarin but have been writing code in various languages since 1968 and have used windows visual studio extensively since the mid 90s. I use a simple, but until now, reliable backup method for developing new projects. I store the complete project in a dated folder. When the project is running and I wish to make a change I simply copy the entire contents of the folder into a new one and work from that. That way if I really mess things up I can get back to a working version.
I have used vs 2019 to create an out of the box Xamarin project in folder "A" and modified the mainpage.xaml "Welcome to Xamarin" message to read "This is project A" and ran it successfully on an Android emulator. So far so good. Now I copied, using windows explorer, the entire contents of folder "A", which also includes the .sln file into a new folder "B". I open "B" with visual studio and change the "This is project A" label in mainpage.xaml to read ""This is project B", rebuilt and executed the program. In the emulator I expected to see "This is project "B" but instead "This is project A" appeared. I suddenly have two versions of mainpage.xaml and don't understand why? I am obviously missing something but don't know what it is.