A user is unable to see the devices that are present on the network after...

Comprehensive and Detailed In-Depth Explanation:

In Windows, when a user changes the network type from private to public, network discovery and file sharing are disabled for security reasons. Public networks are treated as untrusted, and devices on the network are hidden from the user.

B. The Windows Firewall from on to off – Incorrect. Disabling the firewall does not block network visibility.

C. The UAC level to its highest level – Incorrect. User Account Control (UAC) settings control administrative privileges, not network visibility.

D. The file-sharing permissions – Incorrect. File-sharing permissions only affect access to shared folders, not network visibility.