Unless someone has used a Yubikey here, it is unlikely you will get an answer. That’s why I’m asking on the Apple board. The 'Ready to scan' pop-up will appear, then tap your YubiKey to your iPhone.Already did that.

If you do not see a 'Ready to scan' pop-up, tap 'Read OTP Again'.If you see a 'Ready to scan' pop-up, tap your YubiKey to your iPhone.Install AuthLite NFC, available in the App Store.(Security Key NFC not supported) Follow the steps below: The iPhone 7 - iPhone X model phones do not support background NFC NDEF tag reading (requires iPhone XS and later) so a third party companion application is required to use OTPs. The OTP code is passed to the SURFsecureID validation server.You should see your Yubico OTP code pasted into the field. Tap the 'WEBSITE NFC TAG' taking you to a shortcut URL in iOS Safari.Hold the YubiKey 5 NFC or YubiKey NEO to the top of your phone or near the camera (you may need to experiment with positioning depending on phone model).Log in using your username and password (if requested).Go to the website requesting SURFsecureID authentication.

If you have an iPhone that supports background NFC NDEF tag reading (requires iPhone XS and later) and would like to test your NFC-enabled YubiKey (Security Key NFC not supported) on iOS, follow the steps below:

The long description is here: Using iPhone XS and newer It depends on the model of your iPhone how this is done. If you have an Yubikey with NFC capabilities, and your iPhone also supports NFC, you can use an app to read the OTP code from your Yubikey, and past it to the SURFsecureID website when asked. Here your yubikey acts as an keyboard, and types an OneTime Password. There are Yubikeys Available that (also) have a lightning connector to connect them directly to your phone. For many institutions, only OTP is activated. SURFsecureID supports two of these techniques: OTP en FIDO2. Yubikey offers different techniques to authenticate safely.

Yubikey 5c nfc ios