Feel free to try it by yourself. Nothing easier than that. Reboot your phone and try to find it via Find My Device or ring it, without to enter your password before. It will not work.
BTW: it doesn't make sense to exclude security and privacy related things from encryption. Otherwise there would be an unusually high risk to compromise this sort of data.
Find My Device is completely useless until the device is unlocked. As long as it is rebooted and not unlocked, there is no way to detect its location. Since most phones (if not all), use an encrypted filesystem. With such, no service can't start if the device isn't initially unlocked after reboot, including Find my device.
This isn't only a issue with Google's implementation, it's the same with other implementations to.
Since a lot of API's are missing on Android and others have unresolved bugs since age's, it's no wonder that Extension developers are total unmotivated to bring more effort to migrate their extensions to the Android platform.