General Possible Fix iCloud for Windows Sign-In Error / Authentication Loop
If you've been trying to sign into the iCloud app on Windows and nothing works, you are maybe running into a time-sync conflict like me, between Windows and Apple's servers. Changing your time server to a public NTP pool ( pool.ntp.org ) combined with a specific app reset sequence fixed it for me and 2 of my friends, hope this helps anyone here.
Step 1: Fix the Time Server
- Open Windows Settings.
- Go to Time & Language > Date & Time.
- Click the drop-down menu for Sync Now.
- Change the time server from the default to pool.ntp.org
- Save and exit (do not hit sync yet).
Step 2: Terminate and Repair iCloud
- Go to Windows Settings > Apps > Installed Apps.
- Locate the iCloud app, click the three dots, and select Advanced options.
- Click Terminate first.
- Click Repair.
- Do not open the iCloud app yet.
Step 3: Sync Time and Sign In
- Go back to Date & Time settings.
- Click Sync Now and wait for it to synchronize.
- Launch the iCloud app and sign in.
I hope this helps anyone! I was stuck on this issue for over a week now.