There are a couple of settings that control who can see which incidents.
Administrators can see all incidents, as well as the users setup with "Full Access". The following settings only apply to non-admins and those with "Default" access.
By default, users can only see their own incidents and not the incidents reported by other staff. In the Company Setup, there is a an option for "Access All Incidents". This allows all users to see all incidents, including those reported by other staff. One limitation is that non-admin staff can only edit the incidents that they created and not any other staffs' incidents.
With the "Access All Incidents", there may be a concern that users can see all MUIs that were reported by other staff. If that is a concern, use the "Hide MUIs" option.
In Setup-Staff, users can be limited to only UI and Internal incidents, filtering out all MUIs that were reported by other staff. Use the "Hide MUI" option for this.