Of course.
But you can also buy the cleaning from the gardener every year. He then comes with the blessed brush and massages the surface. ;-)
But seriously, these are coverings for outdoor use. They have to be able to handle that.
It's always up to everyone how they clean their stones.
You can use the Kärcher, but just don't get too close.
The company Rinn (Rinn Beton- und Naturstein GmbH) explained to me that you should loosely distribute water with soap over the surface 1-2 times a year, let it soak for about an hour, and then rinse it off with a garden hose.
My down jacket is also for outdoor use. Still, I take it to the dry cleaner because of the down and don't wash it myself.
People also put face cream on and care for their skin even though the skin can handle it.
A roof is also for outdoor use and can handle everything. Still, it's ugly when it is partly covered with moss or other efflorescences.
Your comparisons are a bit shaky...
What kind of terrace decking is that?
Looks very good!
I don't know exactly. I only know that the color is called "sand."