I don't know what year Mac you have or the video card that comes with it, but in my case, my Intel HD 4300 graphics card that came with my Mid 2012 Macbook Pro is barely enough for 2021. Animated Zoom will be choppy, not smooth.
Try resetting Preferences:
You can also use the earlier 2020 if that did not have this problem and see if a later 2021 update will fix it.
My advice is to go into Preferences > Tools and uncheck Animated Zoom. Scrubby Zoom should be fine.