Apple has made some big improvements to its Find My service ever since it combined Find My iPhone and Find My Friends into a single app back in 2019. One such addition is the ability to track down your iPhone even when it’s powered off, which debuted with iOS 15 in September.
Article source: https://www.cnet.com/tech/mobile/find-my-iphone-how-to-track-down-your-iphone-even-if-its-turned-off/