I have upgraded an Azure AD Connect Server, running in staging mode, to Server 2019 and now I get the following error messages:
When I start Microsoft Azure Active Directory Connect Interface I get "Azure Active Directory Connect cannot proceed further as configuration changes cannot be made at this time" -> The Microsoft Azure AD Sync ServiceAccount is changed during the upgrade from AAD__xxxxxxxxxxxx to NT SERVICE\ADSync. I added the ADSync account to the Administrators group and the ADSyncAdmins group and rebooted the system but this did not help.
When I start the Synchronization Service Manager I Get "Unable to connect to the Synchronization Service". Possible cause is that "your account is not a member of a required security group" -> I am Admin on the system.