You should look more into their security architecture if you’re curious about stuff like this. The way Secure Enclave, E2EE (including the Advanced Data Protection feature for all iCloud data), etc. The reality is that they use a huge range of privacy enhancing approaches to minimize what data has to leave your device and how it can be used. For example the biometrics you mention are never outside the Secure Enclave in the chip on your phone and nobody except you can access them unless they have your passcode. Things like running facial recognition on your photos library is handled locally on your device with no information going up to the cloud. FindMy is also architected in a fully E2E encrypted way.
You can browse their hundreds of pages of security and privacy documentation via the table of contents here to look up any specific service or functionality you want to know more about: https://support.apple.com/guide/security/welcome/web