Unable to sign in to Apple ID/iCloud after Sequoia 15.78

Hi,

Sign-in failures for Apple ID or iCloud on macOS Sequoia are commonly caused by local token corruption, password history mismatches during updates, or virtual machine hardware checks. 

Standard Troubleshooting Steps:

• Verify Password Context: Ensure you are entering the Apple ID password and not the Mac user account administrator password. 
• Reset Keychain and Accounts: Open Terminal and run the following commands to refresh local account tokens:

sudo -v ; killall -9 accountsd com.apple.iCloudHelper ; defaults delete MobileMeAccounts ; mkdir ~/Library/Accounts/Backup ; mv ~/Library/Accounts/*.sqlite* ~/Library/Accounts/Backup/ ; killall -9 accountsd com.apple.iCloudHelper ; sudo reboot

• Toggle iCloud Sign-in: Sign out of your Apple Account in System Settings, then sign back in. If this fails, click "I forgot my password" to reset the token. 
• Check System Time: Ensure Set date and time automatically is enabled, as incorrect time settings can reject SSL certificates. 
• Safe Mode: Boot your Mac in Safe Mode to perform a disk check and clear temporary caches.

Virtual Machine (VM) Specific Issues:

• Hardware Detection: macOS Sequoia restricts iCloud sign-in on unauthorized hardware or virtual machines (e.g., Proxmox, Parallels, UTM) to prevent piracy. 
• Kernel Patching: Users have reported success by patching the kernel to bypass VM detection, specifically by setting kern.hv_vmm_present to 0 in the config.plist file. 
• Version Requirements: iCloud in VMs requires the host Mac and the VM to both be running macOS Sequoia. 
•  For Apple Silicon VMs, you must create the VM using an IPSW file rather than an installer. 
• Legacy Workaround: If patching fails, some users restore from Time Machine or create a new macOS Sonoma VM, connect the Apple ID, and then upgrade to Sequoia. 

Keychain Password Mismatch:

• Some users report that Sequoia updates revert authentication to old passwords (2–3 versions back). 
•  If you use a password manager, try entering a previously used password during the update/installation phase, then update the Keychain when prompted. 

If these steps fail, a clean install via macOS Recovery may be necessary.

I have this problem on my Mac Studio (Sequoia 15.7.8) as well. My AppleID is used successfully on my MacBook Pro 13" (macOS 12.7.6), my iMac 17" (macOS 10.13.6) and my iPhone SE (iOS 26.5.2). On my Mac Studio I could log in to my AppleID in AppStore, TV and Xcode. Logging in to iCloud via the website seems to work as axpected. I tried all of the above, without success. Any ideas?

Sorry, my previous post got shortened somewhat. This is the full message: I have this problem on my Mac Studio (Sequoia 15.7.8) as well. My AppleID is used successfully on my MacBook Pro 13" (macOS 12.7.6), my iMac 17" (macOS 10.13.6) and my iPhone SE (iOS 26.5.2). On my Mac Studio I could log in to my AppleID in AppStore, TV and Xcode. Logging in to iCloud via the website seems to work as expected, but enabling iCloud via the System Preferences creates the infinite login loop. I tried all of the above, without success, which means I cannot use my shared Passwords, Notes, Calendars, Documents etc. Any ideas?

In addition to the above, I tried upgrading to Tahoe 26.5.1, which seemed to go smoothly, but in the end it got stuck, leaving my internal Macintosh HD in a completely unstable state. I tried to re-install Tahoe in Recovery Mode, but that failed as well, leaving me with a computer for which Recovery mode tells me there is no way to revive it again.

Long story short, I ended up buying me a new Mac mini, with Tahoe preinstalled. Activating iCloud worked like a charm, there was a small problem with some internal iCloud settings, but iCloud was able to solve it all by itself. But not under Sequoia.