The thing with GM vehicles is that they seem pretty hit-or-miss when you go get a new one. It very much depends on what you are buying. Longitudinal data simply does not exist until new owners become unwitting beta testers and then hopefully post their rants online 5 years later.
It is not necessarily that they are all doomed to failure, but you are trekking through a minefield. They have all sorts of cars and trucks. Performance vehicles like the Corvette and Camaro. The Silverado and all other derivatives. Their mostly "in-house" vehicles. And there are former "partnership" vehicles like the Corolla and various Suzuki makes.
The thing about reliability is that there is a population of parts made, and companies target a particular failure rate and period of longevity for the part. So, even an unreliable part might last quite a good long time with quite a few owners. A water pump might be built to last 100K. Most people might get that. Others later and a different set of others sooner. GM has cut costs too much on some of its parts even when a slightly more durable but more expensive option was there, like the ignition switches.
Having things that cripple the car thrown at you is an occurrence that people simply do not want to go through, especially within the first 100K. And some models simply are far too risky of a buy. On a population-wide basis in the past the masses voted with their wallets when it came to non-trucks, and generally gravitated to the Japanese big 3 for better reliability and longevity of parts, or Euro cars for luxury and reliability before the Euros started adding tons of fancy tech and complexity to their vehicles. The repair litany would not occur until after 100k rather than before, generally speaking, with those older imports. Stuff that should last indefinitely like steering columns actually do so.
Their trucks are probably better off than their cars, but watch out, the aforementioned wax dipping of the frame has issues. This seems to be a cost-cutting decision from them, as painting, which is what they used to do, would be better. Even a lightly used truck needs the buyer to make sure the frame is inspected.