Garage wall is starting to mold

Well, the question is what is stored in the garage. If it’s just the car, bicycles, and trash bins, then it’s enough to paint the wall with a color that doesn’t provide a basis for mold. Garages, if they are not built and heated like living spaces, are always rather damp in corresponding weather, so a paint on which no mold can grow is appropriate. Mold grows at 45% relative humidity and above. If the walls are not obstructed, then this is normally not a problem in the garage.

An uninsulated, unheated garage will always have dew point problems. To avoid mold, you would not only have to ventilate and heat, but also wipe dust and dry the seals. A car doesn’t really care about that. If it’s only about aesthetics and spore issues, then lime or silicate paint helps. Ventilation alone can even worsen the problem if warmer air enters the cooler garage.

Doors regularly on ventilation position is simply a must in autumn/winter.

An uninsulated, unheated garage will always have dew point problems. You would not only have to ventilate and heat to avoid mold, but also wipe dust and dry the seals. A car doesn't really care about that.

No, that doesn't happen if the garage is fundamentally not airtight, meaning it is constantly ventilated.