My hardware is a Lenovo Thinkpad Carbon X1 4th gen, but as mouse and touchpad both seem to be affected I don't think this is hardware-specific.
When running GNOME on Xorg the pointer moves more slowly than in Wayland. This means I have to adjust my settings when switching between Xorg and Wayland, but even if I turn them up to maximum they're still slower than my desired speed in Xorg.
I'm using Arch Linux with the following package versions, but I first noticed the problem a long time ago, and I think I was using Debian at the time:
Hidpi screen? Fedora has the DPIScale option in xorg-x11-drv-libinput as a distribution-specific patch but we don't otherwise have a good solution for upstream yet.
It is hidpi. That's a good point; it had occurred to me earlier, but I forgot to mention it in my bug report. Thanks for the tip-off about Fedora, I'll see if I can get their patch or something similar working in Arch.
Closing this as dupe of 106785 now, given that one has the more descriptive summary, thanks.
*** This bug has been marked as a duplicate of bug 106785 ***