Edits not saving when exporting DNG files

rfrench. Apple's preview cannot read the Adobe Camera Raw/Lightroom instructioins on how to render raw data. It will simply ignore the rendering instructions and show you just the raw data as interpreted with the system built-in raw renderer. To see the dng file correctly, you HAVE to open it in an Adobe program like Lightroom or Photoshop. If you want to export the image as is, you have to use a rendered file format such as tiff or jpeg.

I just duplicated your process with one exception. The exception was that the converted to black and white was done on a virtual copy of the original NEF raw file. But I don't think that would make any difference. I exported the black and white conversion as a DNG, and opened it with the Windows picture viewer. It was a black-and-white DNG file. I'm using LrC 9.3 on Windows10.

Ok, so I did exactly as you did, You then opened the exported DNG in Preview and exactly as I indicated in my original post Preview in the Mac cannot read and apply the edits you have done in Lightroom and displayed the original file. Try opening the exported dng in Adobe Camera Raw or Lightroom and see what you see displayed. First in LrC, second the exported DNG  viewed in Preview on the Mac.

Please provide some additional info, including a screen capture of the full export dialog.

The exported DNG should have the metadata stored in the file header including the edits you made. The edits are only useful to Lightroom or Adobe Camera raw. What app are you using to view the exported DNG?