You should wash your car at least every 2 weeks.
Although some cars might need washed once a week or twice a week depending on the driving environment and driving habits.
If you do a lot of driving in dusty conditions then you may need to wash your car a few times a week or more often.
But if you drive in normal conditions then usually once a week or twice a week or even ever 2 weeks is often enough frequency of washing your car.
Most people will wash their cars or other vehicles every 2 weeks.
People that drive in dusty or muddy conditions or in snow or in areas where salt can get on the vehicle they may need to wash their car every few days or so to remove the salt.
Also if you live in an area and drive your car or vehicle in areas where there's a lot of road salt or even ocean salt or drive on dirt roads often you may need to wash your car or other vehicle more frequently.
I usually wash my car and other vehicles every few weeks unless the car or other vehicle gets more dirty sooner.
In the winter when the roads are being salted I wash my vehicle every few days when I can do so to keep the salt from rusting the car out.
The salt from roads and in coastal areas can corrode and rust metal and cause the cars metal to start to come apart.
And washing the car or other vehicle often enough also removes the grime, dirt and other contaminants which can damage the paint of the car or vehicle over time.