ThinLinc only supports the classical "stepped" model of mouse scrolling where everything moves in large distinct steps. Modern mice and applications support a more fine-grained model where you get a much smoother and precise scrolling. It would be very nice if this would also work in ThinLinc.
Note that this might now be so much the norm that we are seeing bugs in handling of the classical model: https://github.com/xtermjs/xterm.js/issues/5194 https://gitlab.freedesktop.org/xorg/driver/xf86-input-evdev/-/issues/16