Can't log into iCloud on my Mac

Changing date and time settings , location services , home permissions ( read and write permissions ) is one of the cause that a Mac user cannot sign in the iCloud .

See this article Get help with iCloud - Apple Support

Do you have Two-Factor Authentication set up for your Apple ID? If not, then you may need to set it up before you can sign into iCloud under High Sierra:

Two-factor authentication for Apple ID - Apple Support

Best,

GB

Try setting up another admin user account to see if the same problem continues. Please post back on whether or not this worked. Also try the Safe Mode. Please post back on whether or not this worked.

Isolating an issue by using another user account

Safe Mode - About

Safe Mode Startup – El Capitan. also Sierra

If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor. Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.

Etrecheck – System Information

Might be a corrupt .plist.

Do a backup, preferably 2 backups on 2 separate drives.

Quit System Preferences.

Go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J. When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder. Select Library. Then go to Preferences/com.apple.systempreferences.plist. Move the .plist to your desktop.

Restart the computer, open the application, and test. If it works okay, delete the plist from the desktop.

If the application is the same, return the .plist to where you got it from, overwriting the newer one.

Thanks to leonie for some information contained in this.

Some questions did you changed the read and write permissions in guest , shared , home folder ? changed location , date and time settings in your Mac .

Have you set up iCloud Keychain , do you have iCloud verification code , all Apple ID , iCloud id , web mail address and their passwords in your records .

Have you set up air port utility ( do you have wireless network password In your records ) .

The most important of all is iCloud verification keychain code , please post back .