Joomla Smart Search is one of the important new Joomla 4 features, which brings a lot of quality.
With a “new search”, users can search for most of the site content (articles, tags, users) in a quick and easy way.
Joomla 4 uses Joomla Smart Search only (with the improved codebase.), and in this way replace solutions that were known in Joomla 3.