How to fit 4" rigid aluminum duct vent in between walls when there is an angle brace?
I wouldn't build it that way in the first place. Hiding a dryer duct within a wall and venting it through the roof (I'm guessing here, but that's what it looks like to me) is just begging for nobody to clean it until it eventually catches fire and burns the house down. 

I recently re-did my utility room and discovered an in-wall rigid steel duct just like the one in your picture which vented through the roof. Clearly nobody ever cleaned it due to the annoyance of having to get up on the roof, and as a result it was entirely blocked by lint and dust, with a bunch of creepy-crawlies living in it due to disuse and abundant organic material during an unoccupied period. Not only that, but a section of the ducting had gotten open and was depositing moist air right into the wall cavity, which eventually invited termites into that wall:



Do the world a favor and don't hide your dryer ductwork inside a framed wall and vent it through the roof!