For example, the Passat 3B and later platforms introduced proprietary screws for the wheels and brakes, so you weren't able to change them yourself.
Same for all kinds of sensors that will go rogue when the car is turned off and you change a sensor on the engine. All firmware gradually was modified each generation to allow less modifications and less self repairs, and less repairs by third party workshops.
Also, the Golf 2 platform for example had a very sturdy engine running beyond 1 Mio km easily. What do you think happened with the Golf 3 engine design? They made the camshaft structurally weaker, so the engine will blow up more easily. The rest of the engine is almost identical. Talk about being bad at hiding planned obsolescence.
There's many more examples like this, acrosd every manufacturer. The real reason why there is so many people on race tracks driving old cars is because they're easier to modify, easier to maintain, and easier to buy replacement parts for.
It's ridiculous if you think about it, and really frustrating that there is no legislative intervention against this.