public static CreateProjectSettings GetDefaultProjectSettings()

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

  // Use project
}

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

  // Use project
}

{
  //Get Pro's default project settings.
  var defaultSettings = Project.GetDefaultProjectSettings();
  var defaultProjectPath = defaultSettings.LocationPath;
  // 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 ??= Path.Combine(
              Environment.GetFolderPath(
                   Environment.SpecialFolder.MyDocuments),
              @"ArcGIS\Projects");
  // Use defaultProjectPath;
}