Apple has rolled out a new AirTag firmware to enhance the unwanted tracking alert. The update version 1.0.301 tunes the audible alert on the unwanted AirTags it detects, so it'll be easy for you to find it. This feature works with iOS 14.5 or later.
As 9to5Mac noted, this update is being rolled out in phases, so it may or may not make its way to you yet. To get it, make sure you have the latest version of iOS, and your AirTag is within the Bluetooth range of your phone.