Oh but that's not all - the switch itself broke off the metal case of the fan the moment I have tried to turn the plastic shaft! This is how a 40€ "quality" product looks like, apparently.

The plastic of the switch is so brittle it is falling apart at the slightest touch. Aliexpress sells these switches for 0.43€, delivered. I wonder why...

But hey, the metal can of the fan is at least earthed, even though it uses wire nuts for connections inside (is that even legal in Germany??). 3/3