Find My Mac missing from iCloud / Find My app — fixed only by macOS reinstall

Find My showed as enabled in System Settings but the device was missing from iCloud.com and the Find My app.

Tried toggling Find My, signing out/in of iCloud, creating a temp admin account, and checking SecureToken — none restored visibility.

Fixed only by reinstalling macOS from Recovery (over the existing system) and then signing back into my main account.

After the reinstall the Mac appeared immediately in iCloud and Find My and Play Sound works. Good temporary fix - but don't delete the new temporary admin account otherwise you will go back to square one.

Please investigate a possible broken link between iCloud device registration and SecureToken records and provide a repair/diagnostic tool to avoid full reinstalls.

Macbook Air M3, Tahoe 26.0.1