Target Display Mode with USB to Lightning cable
Can I use a USB to Lightning cable to connect an iMac 21.5" (Mid 2010) to a Macbook Pro (Late 2013) for Target Display Mode?
Can I use a USB to Lightning cable to connect an iMac 21.5" (Mid 2010) to a Macbook Pro (Late 2013) for Target Display Mode?
No. Only Firewire or Thunderbolt. Apple sells adapters if needed.
Use your iMac as a display with Target Display Mode - Apple Support
Your 21.5" iMac cannot be used for Target Display Mode at all.
Target Display Mode with USB to Lightning cable