How do I use my Old 2013 iMac 21.5 as an External Monitor?
What cable do I need to connect my iMac 21.5" ( mid-2013) as an external monitor for my new 2019MacBook Pro ?
iMac Line (2012 and Later)
Please clarify which model iMac you have. I am familiar with the iMac (21.5-inch, Early 2013) and iMac (21.5-inch, Late 2013), but am not familiar with an iMac (21.5-inch, Mid 2013) model. In order to provide a cable recommendation it's important to know exactly which model you have.
Identify your iMac model - Apple Support
Once you've determined the model iMac you have, this Apple article provides additional information on how to use Target Display Mode.
Use your iMac as a display with Target Display Mode - Apple Support
