iMac 21.5" 4K display not recognized?

I am trying to replace a cracked screen on my 2017 iMac 21.5" 4K. The cracked screen worked perfectly—minus the crack. External displays from the Thunderbolt (miniDisplayPort) is working normally.

The replacement display arrived, but it wouldn’t power on. After some testing, I figured out that the new display had some issue powering the backlight, or the new display had a bad backlight.

I went back and forth between the new display and the cracked display several times. Each time trying various combinations of PRAM and SMC resets.

No dice.

Now here’s the stinger: now the cracked display isn’t powering up either—but the external monitor still works normally.

So here’s my question: do you experts think the culprit is most likely the Display Port Cable getting worn out from my constant plugging and unplugging? Or is it more likely I’ve damaged the Logic Board?