I have a newborn baby if my partner smokes weed outside doors closed then showers changes and brushes teeth is this the best he can do ?

Best ???: This is better than nothing. However, The smoke does linger in their clothing, often at a level not noticed by those who go nose blind to the smell. Exposure increases risk for cot death /respiratory infections in baby.

Best is to just stop: Weed is not needed in life. The intentional habit of inhaling burning organic material, combined with various chemicals used in the growing and manufacturing of that material (regardless of whether it is tobacco, marijuana, or any other plant) is bad for the body. Just think about it. Who would intentionally start something burning and inhale the stuff over and over and over?

Not wise: All the steps you mentioned are moderately effective, but not completely. Why risk your baby's health for something that is not only not life essential, but harmful to the baby, you and especially your partner.