I rarely use “Reader View” so your comment alerted me to a change to Brave I’d not noticed; thanks.
Where is Brave’s “view menu” to which you refer?
In this comment @Aa-ron provides guidance to re-enable reader mode; no joy, at least not for me.
I’m aware: not every web page can be viewed using “reader mode”. As a test, I loaded a page in Firefox that displays as desired when I toggle “Reader View”. (An icon in Firefox’s unibox or F9 in Firefox conveniently do this.) No success with that page (or any other) in Brave.