Sorry for the delay, y’all. I’ve followed up with our subject matter experts here and now have more details around which keys, exactly, will no longer be supported following the changes Bitwarden has planned.
TL;DR the only keys that will stop being supported are those that show “migrated” in the WebAuthn settings.
More details:
Prior to 2021, U2F keys were registered with the U2F API. These are the keys that were “migrated” to WebAuthn as shown in the interface. U2F keys registered after 2021 are registered using the WebAuthn API. These do not show that they have been “migrated” and will continue to work following the changes Bitwarden has planned.