I have no idea what the speed is on the Z9. When I mentioned the flash speed above, I meant historically for Canon it's been 180-250, with 250 on the higher end bodies, and I was also under the impression all manufacturer's flash speeds were similar. Canon HSS repeatedly flashes to account for the partially open shutter.

My point was since the shutter movement has such a speed limit, and a object can move across the sensor while differing portions of the sensor are exposed, then a sensor read speed that reaches that level of performance should have the same level of rolling shutter/jelly effect as an actual moving shutter... assuming the sensor values are wiped with the same sort of scan time, approximating the other half of the shutter.

We're reached the point where the sensor read is as fast as a shutter can move.