I just got an Imac Pro 27" and tried to download videos from my Mavic Air Sandisk Ultra 32 GB disk but the Imac will not read the disk - I've tried using both a USB port and a card reader. The Imac does not show them either way.  I'm still able to download to my PC with no problem.  The USB is working for all other things, such as my printer, etc.

Any suggestions on how to get the IMac to read the disks? It's the disk that came with my Mavic Air kit

Lucky you! iMac Pro 27" .. I'm looking at buying one, but want it with 128Gb .. VERY expensive. I currently have an iMac 2010 27" and have no issues downloading stuff from my MA. Can you perhaps try another Micro SD in the Air?