I'm using bitwarden, but it's possible to use passkeys from multiple devices and if it's not available for whatever reason, you can just login with username/password/token/biological probe/whatever you used before. As an example: GitLab gives you both options right from the start, so you can use whatever you fancy in that particular moment.

Did [someone from the Working Group] ever back down from their implied threat to blacklist Bitwarden for allowing for the sharing/export of passkeys?

That really rubbed me the wrong way, and smacked very heavily of "the big players (MSFT, AAPL, GOOG) can do this - you can't".