SSMS registered Servers
You should use dbatools - Copy-DbaCentralManagementServer

This command copies all groups, subgroups, and registered servers from one SQL Server to another. By default, all objects are copied.
To migrate all groups, subgroups, and server instances are copied from sqlserver’s Central Management Server to sqlcluster’s Central Management Server.

Copy-DbaCentralManagementServer -Source sqlserver -Destination sqlcluster