Why does iCloud ask for my Mac account password?
I have installed macOS Mojave on my Mac, and a notification appeared in System Preferences for me to update my iCloud account details (including re-entering my password for the account). I went and did that (https://support.apple.com/en-au/guide/mac-help/set-up-icloud-mh36834/10.14/mac/1 0.14), but then the System Preferences asks me this:
"Enter your Mac password to continue.
The password you use to unlock this Mac is used to access your Apple ID, saved passwords and other data stored in iCloud when you sign in on a new device."
Why does iCloud want my Mac's password? Is this password stored on iCloud? Why would other devices ever want it? What feature of iCloud is this related to?
I can't find any documentation on this behaviour on Apple's Support site, nor in the macOS User Guide on the system itself, or anywhere here (https://support.apple.com/en-au/guide/mac-help/welcome/mac).
May I please ask for an explanation of this behaviour and requirement? I cannot complete my login to iCloud, and System Preferences will continue to complain if I don't comply with its demands. If anyone can explain why this dialogue slip has appeared in the iCloud System Preferences pane, I'd be very grateful indeed!
MacBook Pro (13-inch, Late 2016, 4 TBT3), macOS Mojave (10.14)