Exciting news for Google Pixel fans! The upcoming Pixel 9 series will feature a 'Powered Off Finder' API, allowing you to track your device even when it's turned off.
tl;dr new android version has a feature that lets you upload pre-computed "beacons" to the Bluetooth module. If your hardware allows the Bluetooth module to be powered independently from the rest of the board, it will allow the "find your device" network functionality to work when your phone is off, similar to airtags
Good news: sniffing Bluetooth low energy beacons is cheap and easy. It's really easy to verify the beacons are turned off on demand. There are Android apps that can sniff beacons.