[Lightroom Mac] Should I import both HEIC and DNG files when plugging in my iPhone

I'm new to Lightroom and not sure about the correct workflow when importing photos from my iPhone 12 Pro Max. When the device is plugged and I browse the available files to import there's a DNG and the accompanying HEIC file. Should I be importing both of these files or just the DNG file? 

I don't really want duplicate files. 

Also, thumbnails for the DNG files are not generated. Is that expected?