Linux, Mac, and Windows (i happen to use all three regularly for work, hobbies, gaming), Firefox + Bitwarden.

It's totally possible there's something specific about my situation, or the way it was set up in the first place that enables this, idk, but somebody else replied saying they have the same experience so it's not just me.

And even if it was just me, it's still clearly something wrong on the provider's implementation, because it should not be possible for software to sidetrack the user into a passkey enrollment flow, when that user logged in with a passkey to open the current session.