Hi there. My Name is ***** ***** I look forward to assisting you today with your question.
First of all, Keychain problems are a mess and it will take a lot of time and effort to get it fixed. So please don't rate me bad or poor if my suggestions didn't work. I will try my best to help you to fix the Keychain without actually downgrading it.
Sounds like your Keychain was linked with iCloud and lose its connection. So I want you to do this. Restart your Mac to Safe Mode. To do that, turn off your Mac. Turn it back and immediately hold down Shift key for 20 seconds. This will boot into Safe Mode. Then in Safe Mode, go to System Preferences > iCloud and Sign out from iCloud. This is important to unlink the iCloud keychain (turning off keychain in here won't help)
Once you are signed out, click on Finder icon, then in Finder, hold down Option key on keyboard, click on Go menu and select Library. Then trash the entire Keychain folder. Once it is trashed, just restart your Mac normally.
Then open Keychain Access application from Applications > Utilities folder. Click on File menu and select Create New Keychain. Authenticate with your login/admin password ***** asked.
After that, go to System Preferences > iCloud and sign in to iCloud. Now in here, if asked to use iCloud Keychain, DO NOT use it. Turn it off or cancel it. Then do a restart again.
That should fix it. Please let me know if that didn't work, so we can continue troubleshooting