So... how are vehicles made for videogames?

Todays... 500K +++++ :-) Conventional low poly is from yesterday... that started already a time ago. I have to create new models my models are old school low poly, I call them... anti-next gen.

Simple. We have 2022... years before triple A games used counts around a fraction of what´s used todays. Many AAA racing-games use already a TRIANGLE-count of 500K tris per car. If you develop, you know, that this polycount has to be calculated practically almost x 3 = shadows + collisions. However, todays´s engines nail it and can render it with the right cards without problems.
I have so many car models created years ago, I even don´t dare to offer them on CGT, because they are out of date, with low poly counts that nobody would buy. Maybe some mobile indies, but for low budget.
So my personal advice, if you create new cars, or redesign something, do them for next gen, and at least mid-poly, with all that nice round mudgruards and wheels, and don´t look back to 90ties.

Like I said in my original post "Normal as 16bit for working files and 8bit for optimized delivery format", which means 8bit normal texture for real-time. All my products that have 'PBR' label work on android at fast frame rates, what do you mean nightmare? What if a car is metallic, what's the difference? Should you make it like other people on sketchfab... Again I dont understand, why the comparison to sketchfab? What does it matter how you make the material, as long as it looks like the reference then its good right?

This is a pretty large topic. Car models are usually done using blueprints (if there are good blueprints where views match/align without distortion) if there are no blueprints, camera matching is used. What style, how many polygons, what type of textures , how many textures, what it's roll will be (is it hero car, is it static model, is it cutscene model etc.) depends on the hardaware on wich game will run. When we come to the hardware anything goes, all "old school" methods are pretty much still alive today. For example, if you want to do a car in pbr, you need 7-8-9 textures in order to look good and that need memory, and if platform is mobile phone you usually don't have that memory so you have to be creative. Some designers mix styles, some use "old methods" some write custom shaders etc. When it comes to games, main goal is to look as good as posible and at the same time to run as best as posible on dedicated platoform/s. Game model that run best on everything doesn't exist. If you are asking about game models that will sell here, people usually use unitiy, unreal as their reference engine and start from there. Now days is popular method of baking normal map of the entire car as you mentioned in your post, that normal map can be used anywhere on anything that supports normal mapping this is also done if game studio have time and resources to do it. Imagine you have to do 50 high poly models of cars and you have about 20 employee. Not everyone is Ubisoft and Rockstar. As I said this is pretty large topic it's better to contact me via private message if you have question, it's better than me writing "articles and books" here on the forum. Good luck.

There's an article from a vehicle artist, Karol Miklas that explains how vehicles are produced for games. They've worked on some notable games and even provided a free 3d car model you can dissect for better understanding.

I can't see any links to your example, but the answer really depends on what the intended use of the model is. Yes, most vehicle models start out life exactly how you suggested. They model a low poly profile against some reference images from the front, side, top, and back of a car. From there, the model can be refined with much more detail. The interior can be modeled, or it can just be low poly with normal maps to fake the inside details. If the model is for a AAA game, then the polygon budget can be higher, especially if the inside of the car will be shown in real-time close-ups and actual gameplay. Even in AAA titles, there is almost always a "polygon budget", even for hero models but normal mapping and other techniques can make up for the lack of geometry these days.

If the model is intended for more high end purposes, like TV advertisements or movies, then there may be no limit to the polygon budget because realism and true to life detail is the most important aspect. Since these models are being used for pre-rendered scenes with a renderfarm, most of the detail will be modeled. Also, concept cars are usually created with precision modeling in CAD software like Rhino, where every aspect of the vehicle can be reproduced to specific dimensions to be a digital clone of the real thing. Again, these models are not typically useful for real-time applications because the polygon count is way too high. These types of models would be created with NURBS surfaces instead of polygon modeling to provide the smoothest and most accurate curves, etc.