Just want to add my solution as I had to use an altered method to ones on here.
Firstly I use a Microsoft account and my issue was also stuck at the sign in screen with the PIN issue everyone else has. My issue was a result of doing a recommended BIOS update that I was prompted to do, after I accepted and it ran the update I couldn't get back into windows cos of the PIN issue.
I also had the option for face recognition sign in with my laptop camera, but I have the camera disabled through the Lenovo vantage software so I wasn't able to use that log in either. There was no option for password login for my Microsoft account (I know my password).
I tried a lot of methods and I'm not sure exactly how many contributed to the solution, but I believe it was likely only these 2 that did the trick:
1 - First need to enable the CMD via the sticky keys method from IMQ2 July 28 2021. I also did not need to use any boot disk/drive.
The second part of that method was using sticky keys command prompt to open ms-config and select normal start up. This didn't do anything for me and normal start up was already selected.
2 - The second part which I think fixed my issue was part of another method that previously wouldn't work for me when I was using the command prompt through the troubleshoot screen. This method was found through a link on reddit r/LinusTechTips, under the title < error "Something happened and your PIN isn't available. Click to set up your PIN again." >
In this part I used sticky keys cmd to run regedit, I wasn't able to do the load hive part but I was able to go to the same location in regedit
"Go to HKEY_LOCAL_MACHINE\ssoftware\Microsoft\Windows NT\CurrentVersion\PasswordLess\Device. There there is a key for DevicePasswordLessBuildVersion. Change the value from 2 to 0. This will turn off that "Require Windows Hello" setting."
I did the above instruction but mine was xxx\software\xxx rather than ssoftware because I was unable to load the hive in the previous step.
After doing the above and typing "shutdown /r" to reboot my laptop, when it restarted it finally showed an option for entering a password with the sign-in options which was previously only pin or face recognition. Then I just entered my account pw and it logged in! After this I still had the pin issue but now it would let me change the pin by logging into my microsoft account whereas before it would just be stuck.
If this still doesn't work for you I also had another option I had yet to try from a site called top-password, under the article title:
How to Set Default Sign-in Option in Windows 10
I was hoping to enable password login with that method before the above worked.