What is the status on smooth scrolling on MacOS host with an Ubuntu guest?

**Describe the issue**
When using a trackpad for scrolling, a "scroll down" event is only received (watching with `xev`) after some amount of scrolling.
This means that a small amount of scroll is ignored.
And that significant movement is required to scroll.
And that scrolling is jerky, as it moves in increments of "scroll down by 3 lines".

This has been an issue for many years. I'd like to take initiative upstream if necessary.
Where is the problem? Is the problem with spice / x11 / wayland / libinput / UTM / qemu ... ?
Any details would be appreciated.

The code already has some implementation for smooth scrolling in UTM for the iOS app:
```
- (CGPoint)moveMouseScroll:(CGPoint)translation {
translation.y = CGPointToPixel(translation.y) / kScrollSpeedReduction;
if (self.isInvertScroll) {
translation.y = -translation.y;
}
[self.vmInput sendMouseScroll:kCSInputScrollSmooth button:self.mouseButtonDown dy:translation.y];
return translation;
}
```

the MacOS code has this line, but it's unclear to me if `.smooth` is ever set? I don't read Swift code.
```
func mouseScroll(dy: CGFloat, button: CSInputButton) {
let scrollDy = isInvertScroll ? -dy : dy
vmInput?.sendMouseScroll(.smooth, button: button, dy: scrollDy)
}
```

A workaround would be to send more "scroll down" events and intercept them on the Linux side with a smaller 'scroll down' increment.

Can you say more about the issue, how you are stuck, and if you have tried resolving this upstream?