Remove blur "effect" in Preview when changing pages
Solution 1:
In short: Preview cannot be changed. The problem is not one at the application level, but in the way that MacOS's Quartz engines renders images. For some reason, the OS 'sharpens the focus' of the image over half a second or so.
It may be possible to change the parameters of such animated effects for a given application, but it will only be possible in Preview if Apple's developers have included a mechanism to do so within the app. None is documented and it seems unlikely that Apple would go to such trouble.
If you don't like the effect, then leave Feedback for Apple. You may prefer to use another viewing app, but it will have to use different image rendering libraries from those present in MacOS.
(Apropos of nothing, I'm currently writing a replacement app to make up for Preview's shortcomings, and I haven't found any method of changing this animation. Yet.)
Solution 2:
I am facing the same issue. What follows may not be considered an "answer" by some people, but may lead to an answer I think and I've never seen it mentionned on the numerous web pages complaining about this issue : I've noticed that when you open the pdf not with Preview BUT with the built-in previewer from finder (the one you obtain when clicking on SpceBar when file highlighted in the finder) then you can scroll through the pages (using PageDown PageUpp, or Fn+Arrows) and this ugly effect does not show. This is very surprising as I've always assumed (and I'm not alone I guess) that this builtin finder preview was using the same toolkit as Preview, which is not the case apparenlty.