After enabling the "Search Enabled" flag to an attribute in the Modern UX (e.g.: Description attribute, or a custom String attribute), the search bar in Projects does not return results from that attribute.
Clarity 16.4.1
Global Search is a functionality introduced in Clarity 16.3.1 as Alpha functionality, and currently in Beta (as of Clarity 16.4.1). It is different from the Quick Search that you can find in many Clarity workspaces.
The "Search Enabled" flag is related to the Global Search functionality, not the Quick Search.
After Global Search is enabled, you will see a "magnifying glass" icon in the top right corner of Clarity, next to the Help, Notifications and Avatar icons:
In this screenshot, you can see both Global Search and Quick Search in the Projects Workspace: