public static CreateProjectSettings GetDefaultProjectSettings()

//Get Pro's default project settings.
var defaultProjectSettings = Project.GetDefaultProjectSettings();
//Create a new project using the default project settings
await Project.CreateAsync(defaultProjectSettings);

//Get Pro's default project settings.
var defaultSettings = Project.GetDefaultProjectSettings();
var defaultProjectPath = defaultSettings.LocationPath;
if (defaultProjectPath == null)
{
  // If not set, projects are saved in the user's My Documents\ArcGIS\Projects folder;
  // this folder is created if it doesn't already exist.
  defaultProjectPath = System.IO.Path.Combine(
              System.Environment.GetFolderPath(
                   Environment.SpecialFolder.MyDocuments),
              @"ArcGIS\Projects");
}