Just found a way to add a search bar link to the top menu (2019 theme just allows search bars on footer). The solution is super simple and is here, via James Huff.
Just installed WordPress 5.0. Smooth installation, no issues so far. Now this blog runs 100% Gutenberg. WordPress 5.0, “Bebo” Welcome WP 5, Forbes If WP broke your site A Gutenberg FAQ on Ma.tt Twenty-Nineteen theme Introducing Twenty-Ninenteen