Offline finding is indeed listed as a feature for iOS 15 tho.
Find My introduces new capabilities to help locate a device that has been turned off or erased, as well as live-streaming locations for family and friends who choose to share their location. Separation Alerts notify a user if they leave an AirTag, Apple device, or Find My network accessory behind in an unfamiliar location, and the Find My network now supports AirPods Pro and AirPods Max. A new Find My widget offers an at-a-glance view directly from the Home Screen. - Apple Newroom (iOS 15)