The 4% rule isn't really impacted, but yes you need to consider the money after taxes. Thinking of the 4% rule as the 25x rule (its inverse) is likely easier to get tripped up by this.
That's why there is a tax topic here--taxes are important. If one is diligent in the US, you can take taxes to 0%. Of course, the relative opportunity varies widely on the country you are in, the country you are investing in, and how much money you need each year.