Linux - disable mouse acceleration

Open or create file

/etc/X11/xorg.conf.d/50-mouse-acceleration.conf

Section "InputClass"
 Identifier "My Mouse"
 MatchIsPointer "yes"
 Option "AccelerationProfile" "-1"
 Option "AccelerationScheme" "none"
 Option "AccelSpeed" "-1"
EndSection

If is not working check for installation libinput and remove that all to fucking hell.
Because libinput break crosshair in games, redefine mouse acceleration in display manager and cursor theme too.