I found this fix:

// Read Text test - Read the text from a txt file and add create a new txt file

  // with the original txt file data

  public void ReadAndWriteTextTest()

  {

      // Get the root path

      var webRoot = _env.WebRootPath;

      // Text with this txt file which is a copy of the MS Word document

      // what_we_do_and_how.docm

      var inputfile = System.IO.Path.Combine(webRoot, "What_we_do_and_how ENCODED.txt");

      // The txt file name to be created.

      var outputfile = System.IO.Path.Combine(webRoot, "A6CWrite.txt");

      // RC@202503100000 - Get the 1252 specific code page to use with Encoding.RegisterProvider

      Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);

      // Read the input txt file data

      string inputdata = System.IO.File.ReadAllText(inputfile, System.Text.Encoding.GetEncoding(1252));

     // Create and write to the ouput txt file

      System.IO.File.WriteAllText(outputfile, inputdata, System.Text.Encoding.GetEncoding(1252));

 }

the outputfile now shows the correct encoding :