A cloud-based identity and access management service for securing user authentication and resource access
Hi @Luis Antonio Sánchez Suero
Some attributes must be unique in Entra ID like User Principal Name and proxy address.
To fix this issue sync conflict you should avoid duplicate object in Entra ID by updating the account created in Entra ID or the account synced from on-prem active directory
For more details please refer to the following link:
How to connect health diagnose sync errors
Please don't forget to accept helpful answer