Can't log in into iCloud after installing macOS Mojave on MacBook Pro 2013 Retina
Since you have confirmed that a new user can sign in, your next step is unfortunately to engage Apple technical support. 

You’ve ruled out date and time errors, an error on the network and an error on the cloud side of your account that’s like a lockdown or other massive error. You should expect to be requested to make a support pin to indicate that you allow Apple engineers to support you with your personal data.