A username and password has been the main way in which people use IT for decades. The username being your identity and the password being a secret that only you know. The username is often public. A typical example being your email address. Your password is private but depends on you choosing something that can't be guessed or is complex. The word "password" is not a good one.
Essentially this means that the security of your personal data comes down to one word. Your account can be accessed by anyone who knows the password or can guess it or has software that can just try combinations of numbers and letters to guess it.
Its hardly surprising that many additional security methods have been added to the mix over the years. One popular addition is a Personal Identification Number (PIN). This typically has 4 to six digits. Another is a second factor or multi-factor authenticator. This could be a key fob or app on your phone. Another is a one time password (OTP) sent to your registered phone by text.
A key fob in your USB slot of your PC can also act as a password or authenticator. The FIDO standard now defines a common standard for these kinds of physical security devices.
All of these improve security. However, a lot of people just find them annoying so tech companies have been looking for something better.
The Microsoft solution is Windows Hello. This first appeared in "beta" with the 2015 Lumia 950 Windowsphone. This came with an iris scanner. The lack of success with Windowsphone means that you now see it on PCs.
Face ID works well. As you look at an iphone it simply unlocks. No fuss. No passwords. Many applications now support it. Your ID stays on your device so it's private.
There are videos about twins fooling Face ID. However, this is a rarity. The main problem in 2021 is a global pandemic. Wearing a face mask has become normal and using a fingerprint is now better than using your face.
Rumour has it that Touch ID is coming back to the iphone. Whether this is later this year or means it will be in addition to Face ID is unknown. The problem is that for iphones sold in the last couple of years Face ID is now annoying rather than convenient when people wear a mask.
Apple are known for expensive solutions. So the new update to IOS 14.5 is expected to bring a new unlock method for iphone to get around the problem of Face ID not working. Being Apple the solution is using an Apple watch for authentication.
To do this you need an Apple Watch. We are a long way from simple passwordless solutions promised by bio-metrics. The Covid-19 pandemic is throwing up some strange consequences. Iphone users buying Apple Watches is just one of them.