When Microsoft Exchange Server Setup prepares domains for Exchange Server, the “initialize domain permissions” process tries to find all RODCs in each domain to apply certain permissions to them. Even if the RODCs are configured for OU=Domain Controllers, users can’t find them if they are in any other domain other than the one in which Setup is running.
This issue occurs because the code in IsRODCType creates a DirectorySearcher class to find the RODC by name. However, the code does not specify a search root either in the constructor or following it. Therefore, the DirectorySearcher searches in only the domain in which Setup is running.
To fix this issue, install Cumulative Update 12 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.