[LachlanHunt]

Use a 3rd party password manager with Passkey support like 1Password or Bitwarden for the most broad cross-platform support. You can't currently export and import passkeys between different implementations, so if you wanted to switch from Apple iCloud to Google, for example, then you'd have to go to each site and register a new passkey on each of them with your new password manager.

The FIDO alliance as supposedly working on a way to securely transfer passkeys between different password managers, but that's not here yet.