Toyota for some reason does low voltage for their HVAC screens. My brother's RAV4 is the same thing, only his is worse b/c when you wear polarized sunglasses, the screen completely disappears. FAIL. In my 4Runner, they don't, nevertheless, it's very dim.
Only tried and true way is to do the 12V mod. Basically you hard wire (one way to do it) the 2 LEDs that light up the HVAC screen to a powered wire (pick one,l I wired mine to the radio power) to get the wanted brightness. You loose dimming, but that doesn't appear to bother anyone.