With e.g. a YubiKey 5 that tool more or less finishes with “successfull” ***. Could you please explain in what way the outcome would be different with an old non-FIDO2 YubiKey to be able to compare it? 
And regarding @kpiris 's tests I would like to ask whether you can enlighten us about what exactly happens (= what kind of credential get’s created), when you had only FIDO U2F enabled on a YubiKey (i.e. every other protocol disabled, including FIDO2) and obviously can successfully register that key for the FIDO2-2FA-Bitwarden option? (especially because according to the Bitwarden documentation one shouldn’t be able to create a “FIDO1” credential here any longer…)
*** PS: Oh, thanks to @grb 's post below, I now learned at least that you can see the “technical details” there also. 