It depends. It depends on if you are creating a .Net Framework app, which has by default an
app.config[
^] file; or if you are creating a .Net (core) app, which does not. There are other differences, like the .csproj file and more.
The same code will work in both Frameworks, .Net (core) is newer, will run faster, and can also have a config file, named
appsettings.json[
^], however not required by default.