I would check with the lab that they can read DNG in PS or LR. The safest method is to open the file yourself in PS and export as tiff. Then send the tiff file to the lab. They may even prefer a full size jpeg.
Is there another app to see the file aside from Photoshop (i.e. anyone know why Preview won't show the settings?)
In order to display a raw file with edits, the image viewer would need to be capable of first doing the raw conversion, then reading and interpreting the edit information in order to apply them to the converted file. Simple "viewers" such as Preview are not capable of doing that, instead they typically will extract and show you the jpeg which is embedded in most raw files, which of course is embedded by the camera at the time of capture and so will not have been updated to reflect subsequent edits.
If you are sending to a lab, DO NOT SEND THEM dng. They will not be able to print it. Very few labs use photoshop and very few will be able to read the settings. The sRGB jpeg you export from Lightroom CC is more than good enough to get the highest quality print. If you want the best quality print, you shouldn't use Lightroom CC but Lightroom Classic or Photoshop but the sRGB jpegs from CC will print just fine for almost anything you want to do. Don't worry about the file size. With jpeg files it is NOT indicative of the image quality.
Hi, do you know if there's a significant difference in jpeg image quality when exporting from LR classic vs LRCC? In what instances would you be able to tell the difference? I always thought file size was indicative of image quality, and when I export jpegs from LR classic, the file sizes are typically 2x larger than jpeg exports from LRCC; I'm a bit confused.