I cannot use iCloud on Windows

Actually I use win11 but I don’t know why view “windows6” in here .

See this Apple article: Check your Apple ID device list to see where you're signed in

https://support.apple.com/en-us/HT205064

Remove the Windows 6 PC and add the Windows 10 PC.

Do you still use Windows 6?

Windows 6 is Windows OS Vista (Januari 2007) is an outdated OS, is an unsupported version of Windows

Microsoft say goodbye to Vista in 2017.

See this Apple article: System requirements for iCloud

https://support.apple.com/en-gb/HT204230

You need to use Microsoft Windows 10*

If you use Windows 10, see this Apple article: If you can't connect or sign in to iCloud

https://support.apple.com/en-us/HT203512

“Unable to login to iCloud.

Sign in to iCloud because there was a problem authenticating this Mac

you can't. Try restarting your Mac and logging in again.”

Is that also solved?

You have Check your Apple ID device list to see where you're signed in

https://support.apple.com/en-us/HT205064

When a Mac is listed, remove it.

There is a another complex situation.

Let us know what that another complex situation that is.