The update was recently released where it introduced a bunch of changes and new features to iOS, one of which is the full support for physical security keys. This means that if you have a FIDO2-compliant security key, you should be able to use it with your iOS device. Prior to this, iOS apps had to individually add support for a Lightning connector on the YubiKey 5Ci into their apps, but now users won’t have to.
For those wondering what are security keys, basically these are physical devices that authenticate users when plugged into a device. Yubico is a company who has created such security keys in the past, along with companies like Google who are also selling their own security key.
The security key method is a lot more secure compared to passwords because in theory, no one else should have a copy of your security key, so even if your username and password is compromised, they still would not be able to login.