is momentum still conserved when a car drives into a brick wall? and how?

The momentum is absorbed by the earth which moves.

It will depend on how you define your system. If you define the system to be the car only, then no, since an outside force acts on the system. If your system is the car the wall and the Earth, then momentum is conserved.

The momentum of the car is transferred to the earth. So the earth's velocity changes. But the mass of the earth is so big compared to the car's, that the change in earth's velocity is too small to notice or measure.

Overall, the total momentum (car's + earth's) is unchanged, so momentum is conserved.

Speed of brick wall = 0. Therefore momentum = 09.

Yes. The wall is attached to the earth whose mass is so much greater than the car's that the change of the earth's speed is insignificant.