@Abdul Ziyad, UAE Thank you for reaching out to us, As I understand you are getting this error 0x8023134a attribute must be unique for one of the user account during the sync cycle.
Error description which you are seeing on the AD Connect server is self explanatory, attribute which is throwing this error, must be unique. Make sure no other object in the Azure AD has the same attribute synced to another user account.
Refer to this https://learn.microsoft.com/en-us/troubleshoot/azure/active-directory/objects-dont-sync-ad-sync-tool which has the steps/process to identify the object.
Let me know if you have any further questions, feel free to post back.