I want to add blur to dock like the MacOS dock. Trying to get this MacOS blur dock effect:
Unfortunately, the dock doesn't support background blur on GNOME (the functionality is just isn't there). See the linked issue for more information.
You can however, apply the blur effect to the top panel or Dash To Panel (an extension which transforms the panel into a dock) using Blyr* which is an extension which adds blur effect to the panel and/or the overview.
Not quite what you wanted but that's all available right now, as far as I know.
*You need to download the extension from the repository itself and install it manually as the update still hasn't appeared on the extensions site.
**It isn't true blur but it works nevertheless. There are some caveats obviously, for example you can't position the panel to the bottom as it's intended to keep it on top and it looks bad with some shell-themes like Flat Remix.