I must have got away lightly as we routinely take my M1 Macbook Air (and before that a much older Intel silicone MacBook Pro) along with iPads and Kindles when we go on our summer European road trips (including to S.France, Spain, Croatia and Greece) and have never suffered any noticeable damage apart from my mobile and Kindle which got too hot on the beach a couple of times but both had enough sense to shut themselves down to cool off. There's a small and handy spot where I stash the laptop in the van but it's higher up rather than down in the depths of a potentially cooler cupboard. I'm not sure whether it makes any real difference but we do have privacy glass in the back (I think 80% light transmission), external silver insulated winsdsdreen and front door window covers and light(ish) grey pop top canvas. Also when we're pitched in hot weather, we generally try to find a spot with some shade and leave front windows open slightly (but the gap is hidden under the wind deflectors and covers until you get close up close), leave a tailgate stand off in place at the back and the pop top windows unzipped. The van itself (and pop top) i is Acapulco Blue. Having said all that, on quite a few occasions, we've got back to the van after a day out and the inside thermometer has been hovering around 48°C when we first open the doors so I've no idea whether our precautions are making any real difference. Plus, despite my saying that the laptops showed no apparent damage, I've really no idea whether their lives were perhaps shortened by suffering the high temperatures but I wouldn't be surprised.
I doubt if any of the foregoing really helps except to suggest that maybe you just got unlucky with your laptop. Either that or the latest generation Macs just ain't as good as they used to be. If yours hadn't been a new one, I might have said maybe regard it as an upgrade opportunity but....
