AG
If you are upgrading from Cumulative Update 13 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016 to Cumulative Update 16 for Exchange Server 2016, then there’s no need to run the /PrepareAD or /PrepareDomain. No additional actions (prepareAD, prepareDomain, or assigning permissions) are required.
/PrepareAD or /PrepareDomain. No additional actions (prepareAD, prepareDomain, or assigning permissions) are required.
https://support.microsoft.com/ru-ru/help/4537678/cumulative-update-16-for-exchange-server-2016