How to disable the Password Synchronization from one domain to another and remove the whole password synchronization?
It's very simple to stop the password synchronization in ODMAD. To do that, please access each participating environment, Settings, Passwords and uncheck all relevant options (for Password Propagation Service or for Modern/Legacy in Password Monitoring section).
Please note that PPS and Modern password sync require installation of the plugin on DCs. It's recommended to also uninstall said plugin from the participating DCs. Modern Password sync plugin is only installed on DCs from environment Settings, Domain Controllers. PPS requires installation of the plugin on all source domain DCs.
PS: There's no harm in leaving these plugins installed.