Unable to sign in ti iCloud

Are you running any anti - virus programs? Using a VPN?

Try setting up another admin user account in System Preferences/Users & Groups 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 https://support.apple.com/en-us/HT204443

Safe Mode - About. https://support.apple.com/en-us/HT201262

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. If the log won’t post, try posting it in Pastebin and provide a link in a reply. After pasting the report in a PasteBin page, go to the top of the page, and copy the address in the URL bar. Paste that in a new reply. Pastebin. https://pastebin.com/

Etrecheck – System Information. https://apps.apple.com/app/etrecheck/id1423715984?ls=1&mt=12

Web site version if required. https://etrecheck.com

In settings choose network

-choose the type of Your connection wifi/ethernet

-go to advanced

-choose DNS

-click unlock

-click +

-add google DNS 8.8.8.8

-click safve

-try to log in

-it looks Your port is blocked to iCloud server

You are welcome. I don't see anything in the report that should be causing problems.

Some people have solved this by going to System Preferences/Internet Accounts, selecting an iCloud account there, and signing in. You need to repeat this for each iCloud account.

Have You try in safe mode?

Try a different browser too.

And in new admin test user too?