You need to have more than one staff record to see this feature, or else new clients will see no staff to book with. Alternatively, you could stop new clients from booking online.
To hide a staff member from new clients, within Settings > My Business, click the pencil (edit) button next to their record, followed by Hide [name] from new clients:
Set the Hide from clients who sign up after date and click Save at the bottom of the form:
VIP clients can still book with them, and all clients must log in before booking.
You can see when a client registered on their record, under Overview > Joined at:
If you have Cancellation Watch enabled, a new client that signs up to it without preference for a staff member can receive notifications for appointments with hidden staff and be able to book with them.
The purpose is to maximise productivity by helping to fill last-minute cancellations as soon as possible, regardless of whether the staff member is hidden from the new client.
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How to stop new clients from booking online - Prevent new clients from making appointments and control which ones to allow through.