You misinterpreted what I wrote. Yes, you can use your Yubikey as a passkey for Bitwarden 2FA.
Based on the symptoms that you have reported, I based my advice off the assumption that in your initial attempt to set this up, you actually selected the “PIN” option in the Windows Security prompt when you were attempting to register your Yubikey as a Bitwarden 2FA passkey (this is the most likely explanation for why you were later prompted for — and were successfully able to authenticate using — your PIN).
Therefore, I recommended (and now recommend again), that you return to the Bitwarden Two-Step Login setup, and delete all passkeys previously registered. I also recommend that you delete the Yubico OTP 2FA that you just enabled.
After you’ve cleaned up the previous mistakes, go back an re-register your Yubikey as a FIDO2/Webauthn passkey in the Bitwarden Two-Step Login setup. When you click Read Key and see the Windows Security prompt, make sure that you click “Use another device” and then select “Security key”. Follow the prompts to register your Yubikey.
In your step-by-step description of what you did, your error is in Step 5 (and everything that follows). When you get to Step 4 (the Windows Security “Making Sure It’s You” prompt), you must click “Use another device” and then select “Security key”.