Would like to bring to everybody’s attention that FIDO2 (The standard that is used for 2FA) actually supports offline mode, and almost all authenticators implement it.
You can use this to derive a shared secret between bitwarden and the yubikey to lock and unlock the database.
Microsoft Hello uses this for offline login; for example
More context: https://groups.google.com/a/fidoalliance.org/forum/#!topic/fido-dev/tosNJvfjMBM