I think it's worth mentioning that FindMy consists of two distinct "networks"; there's the one where other Apple devices find your stuff, and another where your devices upload their locations straight to Apple. The FindMy app combines these two networks to show the most recent location. As far as I can tell this project only uses the former network, which would require an explicit backdoor due to the way it is designed. But if you're trying to defend against government agencies, that latter network is probably more of your concern.