The Pro Display XDR is 7.48 kg and a $199 Ergotron LX Pro is rated up to 10 kg, so that's a fifth of the Apple stand's price.

And looking at Amazon.de listings, it's definitely possible to buy a cheap arm that's good for 7.5 kg. A "suptek Monitor Mount" is good for 10 kg according to the listing: https://www.amazon.de/dp/B0833NQ8CR