Can not sign out of iCloud before selling my MAcBook

When your Apple ID account is deleted, your account details and the data associated with your Apple ID are permanently deleted from Apple’s servers. You can't sign in to your account, and you won’t be able to access any data, content, or services that were associated with your Apple ID.

Before you request deletion of your Apple ID

We recommend that you take a few steps before you request deletion of your Apple ID. 

• Back up the data that you store in iCloud—including content for any Apple or third-party apps that store data using iCloud—to a place that doesn’t use your Apple ID for access.
• Download any DRM-free purchases, iTunes Match tracks that you don’t have copies of, and any other music and media.
• Review any active subscriptions. When your account is deleted, subscriptions are canceled at the end of their billing cycles.
• Save copies of any Apple-related information that you currently need or expect to need.
• Make sure that you sign out of all your devices to avoid issues with apps that use your Apple ID account or iCloud. After your account is deleted, you can't sign out of iCloud or turn off Find My iPhone Activation Lock on your devices. If you forget to sign out, you might not be able to use your device when your account is deleted.
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Note : you have started the process of deleting the account from server , however once again tried to sign in with your Apple ID and password from Mac at www.icloud.com using 2FA , also the signed in devices like iPhone / iPad second Mac are not removed .

You have to stop it , by revealing alfa numeric code to apple care senior advisors before 30 days , once the account is recovered .

The other devices iPhone / iPad or second Mac that are signed in with same Apple ID and password on the same network with Mac has to be removed View and remove your devices that are associated with Apple ID purchases - Apple Support

Then you will be able to sign out properly Apple ID from system preferences of concerned Mac Sign in or out of your Apple ID on Mac - Apple Support

What to do before you sell, give away, or trade in your Mac - Apple Support

macOS Ventura or later: Choose Apple menu  > System Settings, then click your name (Apple ID) in the sidebar. On the right, scroll down and click Sign Out.

macOS Monterey, macOS Big Sur, or macOS Catalina: Choose Apple menu  > System Preferences, then click Apple ID. Select Overview in the sidebar, then click Sign Out.

Earlier versions of macOS: Choose Apple menu  > System Preferences, click iCloud, then click Sign Out.

When asked whether to keep a copy of your iCloud data on this Mac, you can keep a copy, because you will erase your Mac later. Your iCloud data remains in iCloud and on other devices that are signed in to iCloud with your Apple ID.

I should have stated that this MB Pro (2011).

First check the account status on server using this link https://iforgot.apple.com/appleid#!&section=appleid

Enter the Apple ID password , the character displayed , and rest of credentials for the account if green check mark appears it means account is verified , sometimes if the account is zero on the server account , then you have to contact apple support senior care advisors so that they might update it .

Note : may be Apple ID is signed in Mac Pro ( 2011 ) , and the Mac is being idle the most important is the status of the account on server .

When the account is verified , so that Mac should be signed out leaving all devices iPhone / iPad ( these will be intact and not signed out , Mac will then stop syncing with iPhone / iPad .

Signing out Apple ID is done from an individual device hard ware address , suppose a Mac is signed out , the other devices will not be signed out .

It’s not clear to me why you signed into iCloud again after ‘clearing data’, nor what the MB Pro machine is. Is that the one you are trying to reset and then sell? Why choose to keep the data on that Mac if you’re trying to reset it?

I also note that you were _not_ trying to delete your account so I am baffled why that was discussed.

I'm wondering if I can go ahead & just erase this old Mac & reinstall macOS using Disk Utility. I've done it on a couple of other apple devices.

Yes you can .