For two-finger scrolling to work consistently in GNOME Wayland, I have to place one finger on the touchpad before the other. In addition, the point of contact of the second finger must be higher than the first’s.
I observed this behaviour with a Lenovo ThinkPad. I cannot say whether it is unique to this laptop or it is by design in GNOME Wayland.
UPDATE 29/06/2022: Two-finger scrolling appears to be improved on latest testing release. I no longer have to be so precise when touching the pad with my fingers.