Hello,
Thank you for posting in Q&A forum.
If you’re unable to add a user on a Domain Controller because the Add User or Group button is grayed out in User Rights Assignment, you can try either of our recommended solutions below to resolve the issue.
1.Modify default Domain Controller Policy setting
2.Enable Add User or Group button in User Rights Assignment
See the following links for detailed descriptions of the relevant processes for each solution: https://www.thewindowsclub.com/add-user-or-group-button-is-grayed-out-in-user-rights-assignment
I hope the information above is helpful.
Best Regards,
Yanhong Liu
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