Driving as Exercise

I have my setting at sedentary so I'm curious if it's legit at all to add driving when it's a significant part of a day.

I know it takes a great deal of concentration and can leave one mentally tired. I also know that the brain uses 25% of our daily energy, but I don't know whether energy use fluctuates based on how hard one is using their brain or whether brain energy consumption is just constant.

Yes it is legit to add driving to your exercise diary. That's why it is an option on the list of exercises.