How can I tell the if the HDD flex cable is compromised?

Here’s a good write up! What is SMART and how to use it to predict HDD or SSD failure

Frankly, when I put in a new SSD I always replace the HD SATA cable and I place a strip of electricians tape on the uppercase to help protect it from the rough surface of the case. I also use extreme care on how I bend the cable around the corners. I use an old BIC ball point pen ink straw as a forming brake to help me not damage the fragile foil wires within the cable. Many people get a new cable and kill it within 10 minutes! You don’t want to crease it fold it or spindle it!

The 15” system have two plastic mounts where the bottom cover slides into to support it in the middle (mid-plane) These plastic mounts break! And when they do you run the risk of the bottom cover coming down onto the cable like a guillotine cutting it! This is where @mayer solution is important. creating a foam wall to protect the cable from damage. The 13” models don’t have this affliction as the bottom cover rests directly on the mid-plane bar (the better design).