Users are unable to login to Bitbucket on Safari 13 with FIDO2 USB keys for 2FA and receives the error: "You can't log in with this device because your browser does not support U2F security keys."

However, Safari 13 has support for FIDO2 USB 2FA keys as per: https://developer.apple.com/documentation/safari_release_notes/safari_13_release_notes.

As per https://www.yubico.com/works-with-yubikey/catalog/bitbucket/ documentation, FIDO U2F is supported by Bitbucket which is an extension of FIDO2.

Note: FIDO2 USB keys work in Google Chrome.