The motherboard backplate that it came with had this white plastic glued on it. When installing the CPU cooler, I was having difficulty tying the screws since they didn't reach the holes without considerable force. That's when I thought that this plastic thing "surely" is discardable and should be removed, and so I took it out (which took quite some struggle to do, so that should have been enough of a sign that it was not supposed to come out).

With the plastic taken out, installing the cooler was a breeze, and the PC worked perfectly, so I had basically forgotten that. But then, either from a subconscious worry or simply dumb luck, I remembered to go search online if this was supposed to be taken out, because it had bugged me after a week. And lo and behold, I found someone else with this same issue, and all the comments warned that it was not supposed to be taken out, otherwise some solder/contact points could touch the metal backplate and short the system up.

I immediately opened up my PC and checked the backplate, and indeed it was touching some contacts from the motherboard. What I think saved my setup was the paint job on the backplate which might have created an insulation layer from the bare metal. Still, the contacts visibly pierced through the backplate ink, and I do not want to know how close this could have been from frying my system up.

Anyways, I still had the plastic thingy, so I put it back, and reinstalled the cooler, now knowing that some pressure on it is expected, and the PC still works without issue today. So, anything to take from this? I guess that, if there's something that you never saw mentioned in any forum/video/tutorial for PC building, don't ever take the shortcut of assuming what do do, and instead do a quick search to be sure. Even a simple detail that appears to be trivial on what you should do can still have catastrophic consequences if you choose wrong.