can you please advise me, how can I periodically copy users to another user group in different site collection?
- permission level site-admin
- SharePoint server version 2016
One option would be to use Powershell. Create a scheduled task on one of the servers that will get the Users from Group A and then Users from Group B into an array. Compare them and use delta to add (of you need that too) remove. The only issue with that is that the change will not be immediate but in most cases that is enough.
If you would like to immediate change you need to create a web part for user management that will handle sync at the adding event.