Of course, the first step is to try to fix it. A new device costs around 2,000 EUR and the technician from the factory service costs nothing because it runs under warranty/ goodwill if they find something.
What is the seller supposed to do themselves? That is the responsibility of the factory service within the warranty. If the kitchen installer fiddles with it themselves, the warranty is void.
With the dishwasher... I also have a Siemens and yes, it is sometimes quite loud. I also know the problem of tabs not dissolving from AEG, so I only use liquid dishwasher detergent now.
The problem with the cooktop is actually that you can't reproduce the error.
Like with a car. If the master mechanic can't detect the noise during the test drive, what can they do?
In this case, a replacement would actually be appropriate if the problem isn't fixed the third time.
How often does it occur? That also plays a role. Such a cooktop is now basically a computer, it can freeze...
With the microwave, the fan is probably on its way to some earthly place again.
That's unfortunate but can happen.
Have it replaced again, maybe you just got two poor-quality ones.
And with the fridge... the argument "I've always done it this way" unfortunately doesn't hold. You have to maintain your devices as the manufacturer prescribes.
I also can't put diesel in an ID.4 because I've done that with vehicles for 20 years.