I use Arch Linux. When I connect an external monitor to my ThinkPad, the cursor moves erratically on the touchpad. It moves slowly, stutters, doesn’t go where I want it to, or goes past the target. There’s no problem with the mouse. The touchpad doesn’t always cause problems—it happens sometimes, and it’s very frustrating.
do you have both monitors on at the same time? if so it would be worth checking if the problem also occurs if you have only the external display on.
No, I only have one external monitor connectod. When I use the laptop screen and the external monitor at the same time, the cursor moves erratically on both.
idk if it makes a difference but if you deactivate the laptop screen by just closing the lid i’d check if the behavior persists when you fully switch over to “only use external display” in “display configuration” (not on arch atm so they might be labelled slightly differently)
oh and if you still have the option it’d be worth checking if the problem is the same under x11 instead of wayland (might require manual installation)