@ScottHelme
That's why the proposal: "third-party password manager, paired with an independent TOTP app" seems like the the best solution for personal use until passkeys have mature ecosystem.
Authentication is decoupled from OS vendor. Password vault and TOTP tokens exist independently. Even if Apple or Google bans your identity, you keep your credentials, can log in from any browser or OS, and can update your contact email on those third-party services.
I'm no expert, but if I understand the situation correctly, FIDO alliance has draft for transferring passkeys between ecosystems (Apple, Android, Google, Linux,... ) but it does not exist in practice.
It's probably just an attempt in lock-in to slow walk, or refuse to implement these parts.