Can software dim or brighten pixels of an LCD backlight individually?

i think you misunderstand what "dimming' does.

also, most of those dimming softwares don't use hardware dimming, which means the colors go down, but things like the mouse won't be affected.

the best one i've found (for free) is called f.lux

https://justgetflux.com/

it dims the mouse too, usimg Alt + PgDown, but still doesn't make it dim enough for my tastes.

Software does target individual pixels when it displays things like fine lines or characters on a screen

Many video screens can target blacks and bright pixels in different modes.  Most modern HDTVs have settings for preferences, like Normal, Movie, Sports, etc.  Such balancing is done in software that processes the video signal different ways.  This is for zones of the screen, but I doubt it is down to individual pixels.

Also, in setup mode, many video cards can balance the colors and brightnesses so they appear best on the screen.  So the appearance of blacks, and red/green balance can be done for a particular monitor or TV.

in general, the graphics software can not do this.  photo editing software can do this for individual cases, and perhaps for videos as well