There is a red target like a scope crosshair in the middle of my screen.

Bro... I read all that **** just to look at my keyboard and see a little crosshair symbol on my down arrow key. Pressed FN then the down arrow key and the crosshair went away.

Any idea what its use is?

After doing a bit of investigating (after running into this myself), I've found the answer. This is a feature for MSI computers. Pressing the keys FN + Arrow Keys will trigger different actions, and one of them is the red crosshair. The software involved is likely the MSI Center.

The red crosshair is meant to be used in games where certain weapons don't necessarily provide a crosshair. On my laptop, you can toggle it using FN + Down Arrow. Fans can be toggled with FN + Up, Pause/Play with FN + Left, and Display with FN + Right.

Anyways, check out this Reddit thread. It provides more information as to what each combination actually does: https://www.reddit.com/r/MSILaptops/comments/105cwz9/pulse_gl76_what_do_these_icons_on_the_arrow_keys/ 

I know I'm a bit late but just wanted to post this to help people out.

Still trying to figure out what it is. No Idea.

What i did was Go into MSCONFIG and uncheck all the apps i had starting during startup. Red Cross hair disappeared. I then re-applied the check mark on apps that were driver/system stuff. restarted. No cross hair. Kept doing that to all the other apps. No Cross hair. I don't know what app was doing it but i got it to stop by doing this. Hope it works for you if that happens to you. Good Luck!

I had this issue, to get rid of it I had to press FN and Down.

The Down button had a crosshair on it. So that is the button.

i did adjustments on my AOC AGON Pro 27" yesterday and the red cross has appeared.