Global permission to browse users and groups is correct because the user picker only returns accounts that the person performing the pick is allowed to view and that visibility is granted by this global permission.

The setting that controls whether a user can see and select other accounts is the Global permission to browse users and groups and site administrators grant it on the global permissions screen. Without that permission the picker will not return matches even when accounts exist in the directory.

Issue security scheme is incorrect because issue security controls who can view specific issues and it does not determine whether accounts appear in the user picker.

User directory settings is incorrect because directory settings manage where accounts come from and how they are synced and they do not by themselves grant the right to browse users across the site.

Project permissions is incorrect because project permissions control actions within a project and they do not enable or disable the global ability to browse users and groups for the user picker.

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