AUR of https://github.com/marsqing/libinput-three-finger-drag, three-finger-drag feature for Archlinux
git clone https://github.com/pastleo/aur-marsqing-libinput-three-finger-drag.git
cd aur-marsqing-libinput-three-finger-drag
makepkg -si
usermod -a -G input {user}
# reboot/re-login might be needed
systemctl --user start libinput-three-finger-drag # see if it works
systemctl --user enable libinput-three-finger-drag # auto-start at login
to set cursor acceleration during dragging, set LIBINPUT_THREE_FINGER_DRAG_ACC (default: 1.4) environment variable, eg in /etc/environment:
LIBINPUT_THREE_FINGER_DRAG_ACC=4
using :0 as DISPLAY by default, set LIBINPUT_THREE_FINGER_DRAG_DISPLAY if needed