Okular 20.8 and earlier has a feature that I miss badly: the ability to search for results only in the header titles, AKA "Outline" tab in the Evince UI.
But in Evince 3.38, I don't see any search box specific for the Outline, and if I do the using Ctrl + F, it just opens a regular full text search that finds hits anywhere in the document, not only in headers.
In Okular, as I start typing the search box of their outline, it filters only the headers which match the search string, which is very handy.
Created a feature request for it at: https://gitlab.gnome.org/GNOME/evince/-/issues/1555
Tested on Ubuntu 20.10.