Google discover is only available on phones that shipped with UI3.1, so 20 series phones won't get it... For now.
I've got a Note 20 Ultra, my wife got an A72, she got Discover and I don't.
Easy way around it is to use the Google search widget, the "G" icon does the same thing, or if you're phone is rooted there's a file you can edit to enable it.
