Thankyou Abhishek for your timely reply. I tried troubleshooting steps1,2,3,4 but the issue persisted across all browsers viz. Edge, Chrome, Firefox. I use VPN occasionally hence deep dived system services and noticed 'Nord VPN / Mcafee Total Virus protection' background services were running. This caused icloud sync to hit network authentication error. As I QUIT the VPN app and tried again going through steps 1,2,3, 4 the iCloud Sync worked instantly.
I will keep a tab to check if the issue re-occurs when VPN or inbuilt anti-virus VPN is enabled. Hope this helps.