Fix the Identity Management for UNIX Upgrade Block
Windows Server in-place upgrade blocked by Identity Management for UNIX: remove IDMU with DISM or comment out IDMUUpgradeComplianceCheck in compliance.ini.
Upgrading A Server 2012 R2 Domain Controller To Server 2019!
In-place upgrade of a Server 2012 R2 domain controller to Server 2019: run adprep /forestprep and /domainprep first and check the supported upgrade paths.