The sensitivity for an external mouse is really weird, meaning that if you move the mouse too slow it doesn't move the cursor. Changing the sensitivity in settings does not fix this issue. This does occur both with a touchpad and an external mouse.
In the provided recording, I am constantly pausing and unpausing, running my mouse across the screen at a certain speed, and gradually speeding up to show the threshhold.
I also have this issue on my Lenovo Flex 5i (i3-1115G4) with a Corsair Ironclaw mouse. It may have something to do with the game's aim-assist-like function. As a temporary work around, I've disabled mouse acceleration from my chromebook's settings and cranked up the mouse sensitivity in game. The mouse still doesn't feel 100% correct, and in fact feels a bit 'grabby' as you sweep your aim over individual blocks. Nevertheless, this does make the game playable.
Edited for clarity.