I found an article that specifies phone models and explains why[1]. It's iPhone 11 and 12 because it requires a UWB/U1 chip. This thread (via Craig Federighi)[2] asserts UWB isn't the part that's used, but those phones have a newer Bluetooth chipset.

[1] https://beebom.com/how-find-lost-iphone-turned-off-erased/

[2] https://www.reddit.com/r/iOSBeta/comments/otcn02/iphone_rema...

Your hardware needs a low-power mode to activate, before you can activate it.

All of the iPhone “off” features, like express transit cards and find my use dedicated low power hardware that seems to be capable of running the feature without an active CPU telling it what to do.