I updated my Apple ID due to switching e-mails. My iPhones and iPad work fine. However, the windows login screen for the iCloud software auto-loads my AppleID. I can't change it in order to log into the account. I've tried "signout", but that errors and returns me to trying to log in with the incorrect AppleID.
I eventually had to uninstall iCloud for Windows, reinstall iCloud for Windows, then still click through a few error messages since my old username was still auto-populating (but grayed out). Eventually, the logout & login steps worked. Thank you.