Chosen Solution
A repair guy accidentaly broke the cable. Don’t ask how and why… :-/ Is it possible to replace just the cable instead of the whole LCD assembly?
Iľja Pelech yes it is. Take a look and see if this is the cable you are referring to. Check this guide to get to it iMac Intel 21.5" Retina 4K Display (2017) Display Replacement - iFixit Repair Guide
I think yes,the cable is replaceable, I see someone selling the cable in alibaba
