This sounds like an iOS problem. Bitwarden + Firefox on Linux, or Bitwarden + Android, has never been anything but smooth for me when it comes to saving or using Passkeys.

If we go for anecdotal examples that are not representative, then in my case, Bitwarden passkey use ends in an endless loop with most websites. Import and export is still a promise or "coming soon." In the case of hardware keys, two devices are needed. I was a proponent of passkeys, but big players screwed that up, like every single shared "standard".

Bitwarden / ProtonPass + iOS has also been smooth. So sounds like a lastpass issue.