Now there's a post-deployment/upgrade step to be followed post this new LWC version of Metadata Search.
Do follow the upgrade steps as mentioned @ Metadata Search v6.0 : Post Upgrade Steps to start using this new LWC version of Metadata Search.
PS: View Metadata Search, Salesforce quick search app on Salesforce AppExchange: https://appexchange.salesforce.com/appxListingDetail?listingId=a0N30000009wgF7EAI