You can set booking approvers for a calendar during its creation or by editing an existing calendar's settings. For Approvers to be able to approve bookings, they would need to be part of a User Group with Manage booking or Manage calendar permissions.

When a booking is created on a calendar that requires approval, it will be highlighted in orange with an exclamation mark icon.

The Users set as approvers will receive email notifications with clickable links.

The link will take them to the associated calendar booking where they can approve the booking.