public void ShowCustomPopup( 
   IEnumerable<PopupContent> popupContent
)

{
  //Create custom popup content
  List<PopupContent> popups =
      [
          new("<b>This text is bold.</b>", "Custom tooltip from HTML string"),
          new(new Uri("https://www.esri.com/"), "Custom tooltip from Uri")
      ];
  mapView.ShowCustomPopup(popups);
}

{
  if (mapView == null) return;

  //Create custom popup content
  List<PopupContent> popups =
  [
      new("<b>This text is bold.</b>", "Custom tooltip from HTML string"),
          new(new Uri("https://www.esri.com/"), "Custom tooltip from Uri")
  ];
  // Sample code: https://github.com/ArcGIS/arcgis-pro-sdk-community-samples/blob/master/Framework/DynamicMenu/DynamicFeatureSelectionMenu.cs
  var topLeftCornerPoint = new System.Windows.Point(200, 200);
  var popupDef = new PopupDefinition()
  {
    Append = true,      // if true new record is appended to existing (if any)
    Dockable = true,    // if true popup is dockable - if false Append is not applicable
    Position = topLeftCornerPoint,  // Position of top left corner of the popup (in pixels)
    Size = new System.Windows.Size(200, 400)    // size of the popup (in pixels)
  };
  mapView.ShowCustomPopup(popups, null, true, popupDef);
}

public static void ShowDynamicPopup(MapMember mapMember, List<long> objectIDs)
{
  MapView mapView = MapView.Active;
  if (mapView == null) return;
  //Create popup whose content is created the first time the item is requested.
  var popups = new List<PopupContent>();
  foreach (var id in objectIDs)
  {
    popups.Add(new DynamicPopupContent(mapMember, id));
  }
  mapView.ShowCustomPopup(popups);
}
internal class DynamicPopupContent : PopupContent
{
  public DynamicPopupContent(MapMember mapMember, long objectID)
  {
    MapMember = mapMember;
    IDString = objectID.ToString();
    IsDynamicContent = true;
  }

  //Called when the pop-up is loaded in the window.
  protected override Task<string> OnCreateHtmlContent()
  {
    return QueuedTask.Run(() => string.Format("<b>Map Member: {0}, ID: {1}</b>", MapMember, IDString));
  }
}