Last year I bought a new Apple iMac to replace my 11 year old desktop. When I tried to download photos, the new iMac would not recognize both my card reader and the cameras. It sill worked fine on the older computer, so I thought my camera firmware was too old for the new version of IOS.
Today, got over the procrastination, and updated both of the bodies I use. Neither could be seen by my iMac. After a couple of calls to Apple (the first was a dropped connection), I learned that my version of IOS only works through an application called Image Capture. I can now load images directly from the cameras, but not from the card readers. I suspect a new, compatible card reader may solve that.