Working in the aviation industry (before retiring) the biggest issue was bi-metal corrosion and spiders webs, where some components would arrive ready tinned and specification said lead free, but in fact were leaded. Due to contents of each solder being different, they do not mix, and life of joints were reduced from 10 years to 2 years.
In the very early years of the Macintosh (I'm talking about the original toaster shaped Macs) cold (cracked) solder joints were common due to heat cycling and poor cooling. A touch of a soldering pen to the solder joint would cure the problem. Also it wasn't uncommon to see a popped capacitor every now and then. These could be easily replaced for a few cents. I used to install fans in Mac Pluses for users and that would make them super reliable. But that was all about 35+ years ago.
Mostly the hardware problems that I've seen users have since were bad GPU's in some MacBooks (manifesting as an anomalous line or band dispaying on the screen), and, of course, a brief plague of swollen lithium MacBook batteries that usually first manifested themselves as keyboard keys that wouldn't work properly. Both happened about five to ten years ago.
That said, back when I used to do in-person consulting, it wasn't unusual to find that users/businesses had a closet piled high with old retired Macs that never failed. They just got so old that their users wanted a newer flashier Mac, and they couldn't bear to throw away a Mac that still worked and which had served them so well.
I remember one independent Macintosh store in San Francisco called me one day, and I dropped by and they led me to a back room where, upon opening the door I was confronted by a room full of. by then, very old toaster Macs. They wanted to know how much it would be for me to turn every one of them into a MacAquarium!