Facade paint: Should it be painted once or twice?

THIS has nothing to do with the color. Walls that gently release indoor heat to the outside are generally not preferred by algae. Google: algae on [wdvs-fassaden] Fraunhofer Institute

Thank you for the interesting tip! I have now also googled it – the most obvious solution, "infrared paint," apparently is still in its infancy. "The most effective method [to prevent algae growth] according to the studies is the use of IR coatings. These reduce the physical effect that ultimately is responsible for microbial growth. Unfortunately, the currently available IR coatings are not yet sufficiently weather resistant. But the results in this publication show that it would be worthwhile to further develop these IR coatings in order to increase their weather resistance."

THIS has nothing to do with the color. Walls that gently release internal heat to the outside are rather not preferred by algae. Google: algae on wdvs façades Fraunhofer Institute

Good morning Buschreiter. Thank you very much for the hint. Yes, today's façades (insulations) promote growth (keyword cooling/dew point in the plaster).

This is also one of the arguments for the mineral paint. Fraunhofer itself sees moisture on (not in) the façade as the main point for algae. Mineral plaster already works according to the hydrophilic principle (absorbing water to keep the surface dry).
Silicone resin paints practically seal the plaster (lotus effect) and negate the effect. When the lotus effect disappears (which can happen after just one year), water remains on the plaster surface and it rots.
Silicate paint, on the other hand, supports the hydrophilic principle. The surface of the plaster remains dry. This is the effect next to the alkalinity (yes, that also decreases over time), which provides a hostile surface to mold/algae.