Both Android[1] and iOS[2] have both recently gained support for acting as WebAuthn authenticators, supporting authenticating on other devices (Chrome/Safari on desktop gives you a QR code to scan, then the devices communicate via Bluetooth to use the phone as a WebAuthn authenticator). The keys also sync via your Apple ID/Google account. Should go someway towards making WebAuthn a viable replacement to TOTP for people who need to sign in across multiple devices and don't want to buy a hardware authenticator, though more widespread support is necessary I think.

[1]: https://developers.google.com/identity/passkeys/use-cases#si...

[2]: https://support.apple.com/en-gb/guide/iphone/iphf538ea8d0/io...