Increase the maximum acceleration value
I am using Manjaro with KDE and have the mouse acceleration profile set to flat and slider to max in the system settings. Unfortunately that is not fast enough and I also feel like maximum should be even higher than what I want to achieve. So I created an issue on the KDE bug tracker: https://bugs.kde.org/show_bug.cgi?id=401584
Apparently it is not in their hands, so I create this issue.
To me a maximum value that is about three times higher than the current one seems to be appropriate.
Further maybe helpful notes
A short investigation revealed that the slider from KDE seems to affect the
Option "AccelSpeed" "float"
Sets the pointer acceleration speed within the range [-1, 1]
(see https://www.mankier.com/4/libinput#Configuration_Details although that seems to be the xorg related part).
I am unsure whether https://wayland.freedesktop.org/libinput/doc/latest/pointer-acceleration.html#acceleration-factor is the relevant part here which has a "current maximum" of 3.5