Before entering the vehicle walk around back and give it a quick whip. Now you can be sure your not going to run over some baby. If you can not back into a parking spot using mirrors without the camera, then another...um...solution is required.
My lower rear window and taillights are neither protected by aerodynamics nor fitted with washers or wipers, so must be frequently hand washed in my typical winter driving conditions. The camera lens gets cleaned at the same time. Our new Subaru, acquired last week to replace a previous century Subaru, is going to have the same issue.
When driving a friends car I can't look at the display. You cant rely on it for anything more than distance to an object. For me trying to pay attention to normal views and the screen leads to not really focusing. Alsway end up stopping, taking that instant of time needed to forget the screen and continue. More on point most vehicles have rearview cameras now. Honda for one has them on all models and trim except Fit. They all are degraded by water on the lens. The only remedy I can come up with is to have the camera behind a surface in a rear wiper path. Which doesn't work well on sedans for camera placement not to mention lack of reaer wipers on vehicles.
I also think there is a protective film on OP's camera lens that has not been removed. To those who think Toyota should have found a way to keep the lens clean, well, I suppose they could have installed a separate wiper for it but I doubt anyone would be willing to pay for it... Try cleaning the lens with rain-x. It will keep water and dust off the lens longer. Personally, I installed an aftermarket backup camera on mine just to have one (like most other MODs I have done) but I really find it useless, except for a quick glance to make sure there is nothing there out of my normal view. It does help a little with parallel parking as you can come very close to the car behind you without touching it, but that is about it.
wiper/washer, but then, it would be covered in water again. maybe a clear flat cover that could have a small headlight wiper. shouldn't cost more than a thousand bucks or so.
A wiper isn't necessary. If a reasonably protected spot can't be located in wind tunnel testing, then a simple jet attached to the window washer system would suffice. It'd cost a tiny fraction of what the overall camera system already adds to the vehicle price.
I think that requiring cameras in cars is ridiculous, but if you're going to do it, do it right. It would be a trivial engineering exercise to fix the issue. Why bother with a wiper and spray on the rear window at all from your perspective? The camera is there because ostensibly the window is not adequate for visibility. If you can clean one, you might as well be able to clean both.