The Search block already searched your site's other page titles and text as a visitor types, entirely in their own browser, no server round trip for each keystroke. This upgrade is only about how results are shown, the search itself works exactly as before.
A real dropdown
Results now appear in an absolutely positioned panel under the input, floating over the rest of the page instead of pushing it down. It closes automatically when a visitor clicks anywhere outside it.
Keyboard navigation
A visitor can move the highlighted result with the up and down arrow keys, press Enter to go straight to it, or press Escape to close the dropdown, all without touching the mouse.
Match highlighting
Whatever text actually matched a visitor's query is wrapped in a highlight, both in a result's title and in a short snippet of its matching body text, so it is obvious at a glance why a given page showed up.
Tip: Nothing about the block's own configuration changed, there is no new field to set, this upgrade only changes how existing search results are presented.