My dealer explained that the sun sensor was part of a module that included a "multiswitch". All I know is that they replaced the sun sensor/multiswitch and fixed my 2012 trying to boil me or freeze me.
It did not fix the sun sensor problem! The sun sensor on my 2012 was ridiculously insensitive. I could have my sun visor down, my sunglasses on, and all of a sudden it turned on the headlights and dimmed my dash so I couldn't even see it. My 2020 has no such problem. The 1st gen 300 reputedly had an adjustment for the sun sensor, but that sadly went away in the 2nd gen 300.
My 300C (2007) automatically turns on the headlights during the day, but not with brightness of the sun, but with the glare.
It is very sunny here (Perth, Western Australia) and they never come on before about 5PM. But if I go out and sun is at that angle where is very hard to see, my headlights come on, I just assumed that because I was squinting/hard to see, it did it so people could see me.
Maybe not? But here, in that situation, it helps; although, yes, dimmer dash lights. With the 2007 white dash dials, not a problem.