Road traffic is always very busy in August due to vacation departures and returns with traffic jams sometimes for several hundred kilometers throughout France, but it's mainly during weekends and on the main roads (National Roads with a name starting with N) and autoroutes (highways).
As long as you do not use these roads you will not have any specific problem.
See the official traffic forecast schedule in the pdf file below:
https://www.bison-fute.gouv.fr/IMG/pdf/Calendrier_2024_Bison_Fute_.pdf
For each day there are numbers corresponding to the geographical zones and colors corresponding to the expected traffic.
The southwest is zone number 5
Colors:
Black: Extremely difficult traffic
Red: Very difficult traffic
Orange: Difficult traffic
Green: Normal traffic
Even in periods classified green, from experience I advise avoiding the A20 motorways between Paris and Toulouse and the A62 between Toulouse and Bordeaux
The main difference apart from traffic may be the availability of accommodation.