When trying to access Defender menu in Active Directory Computers and Users, the Defender OU is present, but selecting it does not display the menu.
Defender Console component is not installed on that server.
The Defender Console needs to be installed for the Defender MMC extensions to appear. This can be installed directly on the domain controller, or on another server that has both the Defender Console and Microsoft Remote Server Administration Tools installed.
Note, that you will need to select the "Defender OU" to enable the Defender context menu in ADUC.