My laptop: I7+Nvidia P600. Newly installed Kubuntu18.04(x64) first looks well with full 1080P display but cannot change screen backlight. After I tried to install Nvidia driver, the windows seems to be put into a 125% scaling( just like what happend on my default win10, but scaling on win10 is changeable). And after I have tried to change it in settings, the status bar also went into scaling. Now my kubuntu have some apps in 125% scaling but some in 100% full 1080P content with 125% border(such as firefox). What a mess! I dont think this is caused by Nvidia driver. My backlight is fixed by the driver but I cant change the scaling back to 100%, which can provide a richer content display.

Thanks for your hard experence to understand what I' d said.