Not sure if this answers your question, but you can use a Yubikey for FIDO2 on iOS with any iOS device with a USB port, or use the camera connection kit to make one on a Lightning port device.
Source: I was curious, so I used a camera connection kit to login to Okta with a Yubikey as my MFA last month.
Source: I was curious, so I used a camera connection kit to login to Okta with a Yubikey as my MFA last month.