General - Sprint 171 Update
Features
Restrict new user invitations from Project and Team Administrators
By default, all administrators can invite new users to Azure DevOps. We've added a new security policy that can be used to block Team and Project Administrators from adding new users. Project Collection Administrators (PCAs) can add new users to the organization, regardless of the policy status.

Next steps
Note
These features will roll out over the next two to three weeks.
Head over to Azure DevOps and take a look.
How to provide feedback
We would love to hear what you think about these features. Use the help menu to report a problem or provide a suggestion.

You can also get advice and your questions answered by the community on Stack Overflow.