vCenter Server Preupgrade check result error:
VMDir Replication between partners is not working.Make sure vmdir service is reachable and started in partner nodes and this node before continuing.
VMware vCenter Server 6.7, 7.0 and 8.0
If the vCenter was part of ELM and was not properly cleaned up, there are chances of stale entries of the previous partner. Stale partner entries can cause the above issues.
Make sure no stale entries of old PSCs/vCenters are present in the directory: Determining replication agreements and status with the Platform Services Controller (PSC)
Use the cmsso-util to repoint to a new domain as per the following tech doc: Repoint a vCenter Server Node to a New Domain