dfsrdiag : The term ‘dfsrdiag’ is not recognized as the name of a cmdlet,

Server Core 2025 does not include dfsrdiag as part of the Domain Controller. If you’re using copilot to help it may tell you DFSR is disabled on your domain controller simply because this diagnostic tool is not present, it’s probably wrong. Older server versions (or maybe just servers with a GUI) can install this tool with:

Install-WindowsFeature RSAT-DFS-Mgmt-Con

But in the case of Server 2025 it’s likely you’ll need to install it separately somehow, but the following also includes it. I recommend you uninstaller this feature when you’re done:

Install-WindowsFeature FS-DFS-Replication