Relevant excerpt for those too lazy to click through:
"However, it's also important that passkeys be recoverable even in the event that all associated devices are lost. Passkeys can be recovered through iCloud keychain escrow, which is also protected against brute-force attacks, even by Apple."
See the section titled "Recovery security" in this article:
https://support.apple.com/en-us/102195
Relevant excerpt for those too lazy to click through:
"However, it's also important that passkeys be recoverable even in the event that all associated devices are lost. Passkeys can be recovered through iCloud keychain escrow, which is also protected against brute-force attacks, even by Apple."