I am running Lightroom classic on a new 27" Mac, I use a Nikon D810. When I try to import photo's with the camera or CF card, LRC won't recognize either source, they don't even show up on the source list. I have been using LR for at least 10 years and have never experienced this issue. I only surfaced when I had to download the internet, monthly subscription versions. I initially had trouble downloading them as well but Adobe support took over my computer and fixed all the issues, so I don't think my problem has to do with the initial download of the program.
Does the camera or card reader show up in Finder? Are you able to copy the image files from the card reader to a folder on the Mac using Finder? If so, try importing from the folder using the ADD choice in LrC.