I would like to know if Bitwarden can be secured by the Yubikey via Yubico Authenticator?
I have read instructions for setting Yubikey up via registering of the security key. However that does prevent me from ever logging in to Bitwarden on another device should the situation ever arise that I need to do it in an emergency.(And yes I realize you can register the key on 5 devices).
I prefer the simple yubikey insertion for successful login, but this does prevent that one time where I may not have an available registered device with me to use.
No, currently it is not possible to use only a security device to login to your Bitwarden vault. Yubikeys and other FIDO2 compliant security keys can be used as two-factor authentication devices, but you must still enter your master password.
There is an ongoing feature request here in the community forums to allow security device-only logins, so you may want to check out that thread: