Which natural stone slabs are less prone to moss/discoloration?

No. If it is non-slip, so not highly polished, then something simply grows there. That's how it is.

I consider the belief that frequent cleaning with high pressure causes moss to return faster to be a misunderstanding. If moss was already there, it does come back faster, that is true. If a stone changes due to the high pressure and pores open up, that may be true, but otherwise, for moss, especially as complete removal as possible is useful, since it can regrow from remaining plant parts (which can hold on more easily in open materials than in closed ones).

A powerful enemy of moss is dryness ...

If necessary, something could also be counteracted with a hydrophobic impregnation. The idea - simplified - is that due to the hydrophobicity, less water is present in the substrate, thereby at least hindering and delaying growth. This works quite well on facades, although the individual case should of course be considered. A kind of self-cleaning is often observed here. For example, we have hydrophobized our wall so that water simply beads off. The frost/thaw resistance should also increase significantly. This also works excellently on a clinker facade :) However, it can become problematic if water stands on the substrate due to the hydrophobicity and freezes in winter.

For those interested: I have now decided on granite and gneiss. Both types of stone are dense and non-porous and therefore generally less susceptible to moss and algae. Cleaning with a high-pressure cleaner was rather discouraged by the expert. It is assumed that this actually promotes algae growth. Sealing is also not particularly effective, as the effect does not last long and sealing often has to be repeated (about once a year).

Moss is fact. Therefore, one resorts to the method of cemetery gardeners, Schurocos Moosweg, known in town and country, time-tested and always gladly used.

We have 80x80x5 stone slabs. Details: Color: Bianco fine, homogeneous surface thermally sealed front with natural stone granules in color and UV-resistant color pigments INTRACLEAN for a dirt-repellent surface How is it best to clean these if no high-pressure cleaner is allowed? Then the question... in front of the house we already have greenish spots between the joints.. Is it sufficient to remove these and then possibly apply a joint sealing agent?