Tried it out and it works, but there is an undesired side effect: it will hide all the read rows in the other glyphs as well (Bookmarks, Messages, Preferences)
User Preferences will miss critical functions like Log Out, please see below where ‘read’ functions will be hidden. Only Do not disturb is showing because I haven’t read/loaded it before.
Is there a way to limit it to just the Notifications glyph?