From Xojo Documentation
| This item was deprecated in version 2019r2.
Please use TextOutputStream.Open as a replacement.
Opens the passed file so that text can be appended to existing text.
If no file exists at the specified location, one is created. If the file cannot be created or opened for appending, an IOException is raised. The append is done by calling Write or WriteLine. The Append shared method replaces the deprecated FolderItem.AppendToTextFile.