@Mountain Pond, Thanks for posting in Q&A. Based on my researching, when you sign-in to your user account or unlock the workstation, the last used sign-in method (PIN, Password or Windows Hello) is saved to the registry, and the same will be used the next time. The last sign-in mechanism is stored in the following key, in the value name that matches your user account SID:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\UserTile
You can let users to sign in with PIN and then see if the PIN will be the default sign in option next time.
If not, you can check if auto login is set, If yes, disable automatic login to see if it works.
Hope it can help.
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