And I’m not sure, if this would be a change, Bitwarden could even make - but (in your case) iCloud would have to make it, e.g. by making a distinction between different credentials and/or allowing to save both types in one entry…
Possible workaround: If you made two entries, like 1) “Bitwarden (contains login-passkey)” and 2) “Bitwarden (contains 2FA-passkey)”, you should be able to store each passkey in one of those two entries separately, without overwriting.
(BTW, the same workaround could in general be done for the Bitwarden vault – a relevant feature request to that would be: Allow storing multiple passkeys on one vault item → initially I was sceptical with that feature request, but especially being able to store one discoverable credential (“passkey”) and one non-discoverable credential (typically for 2FA only), would be a use-case for being able to store more than one “passkey” in one vault item…)