I have an intel nuc connected to my TV which I use mainly to watch videos. When I started it up just now the desktop was too big for the screen at the resolution cinnamon had suddenly decided to run, changed to a higher one than before for some mysterious reason. Anyway at the lower resolution everything fits but the backlight is way higher than on the higher one. Why is that? Also there is no control for changing the backlight setting, what would be the best solution? This is a bit strange because this control is in the power-settings on my laptop that’s also running cinnamon.
I think is about your tv screen mode, every tv should have a mode button to change between modes. When I used a tv as monitor I had to choose “zoom” mode, might be different in your tv, but give it a try