User sharing to control which users can see each other
Key Takeaway
If even one user should not see another user's record, set the org-wide default for user records to Private. Then open up access with user sharing rules, manual sharing, or user permissions.
User Sharing controls which users can see each other's user records in Salesforce, for both internal users (employees) and external users (site or portal users). You set a baseline with the org-wide default for user records, then open up access with permissions, user sharing rules, and manual sharing. Admins use User Sharing when some users, often external customers, should not see who else is in the org.
What User Sharing controls
User Sharing lets you show or hide an internal or external user from another user. Seeing a user means seeing their user detail page and finding them in places such as lookups, list views, and search. So when you hide a user from someone, the hidden user is removed from all of those places for that person.
For Experience Cloud sites, User Sharing decides whether all users in a site are visible to each other.