Has anyone competent tested for too-high electrical draw while the car is parked? It means measuring the amperage the battery is putting out while disconnecting all the various fuses and links, seeing each time what effect that circuit has on the amperage. There is probably something drawing too much current, and once found, that can be fixed. The dealer hasn’t done the job, it seems, so maybe it’s time to ask for this specifically there or somewhere else. Has the Toyota dealer searched for any applicable TSBs?
There are auto electric shops. They usually work on electrics that dealers and owners bring to them. You might find one that can put a knowledgeable and methodical person on your case.
Any non-Toyota factory electrics added on? Antitheft? Audio? Those are more likely than factory stuff to present this problem.
If nothing is found wrong, you could drive a lot more or use a battery charger.
Does your Toyota warranty possibly cover this? You could contact Toyota above the dealer level.