Native WordPress Search is not supported on Shifter because that feature requires PHP. To reintroduce that feature, you'll need to add one of the many 3rd party search tools that can be used with WordPress search.
The largest benefit of replacing the native search function of WordPress is improved search results. WordPress native search does not support features like typo corrections, fuzzy search, or faceted search. Any one of these alternatives will offer those features and improve the search experience for your users.
The official WordPress Plugin for Shifter site search is WP Serverless Search. It requires zero-dependencies or 3rd party accounts.
A static search plugin developed by Shifter for fuzzy, fast, and zero-dependency search.
This is one of the most common search services outside of WordPress Native search and it's supported supported on Shifter.
Algolia is a "Search as a Service" alternative to WordPress Native Search offering free to enterprise level pricing. It's a favorite among developers for their rich API and it's simple to get started.