Recently I have seen this happen. You are at the login screen for your computer and when you type, the characters do not fill in the password or PIN box.
After working with this a while the solution is to reboot. After a reboot you should be able to login.
Apparently there is a quirk in Windows where this can occur.
And reboot, seems to be the primary fix for this and many other issues that may occur in Windows.
Hope this helps,
Happy March 2021!!!
Bill