Mount your disk on your Mac.
#returns a list of disks, find yours, could be something like /dev/disk2
diskutil list
# Unmount disk, weird but true.
diskutil unmountDisk /dev/disk2
#takes a while. CONTROL + T shows progress. And indeed, it’s rdisk, not disk
sudo dd if=/dev/rdisk2 of=/location/on/your/mac/pi20191107.img bs=1m